Roronoa Zoro is a member of the Worst Generation, a notorious group of pirates who are prominent figures in the new age of piracy. Zoro is a master of 'Santoryu' or three sword style, having been a swordsman from his younger years.
He wields the swords, Wado Ichimonji, Sandai Kitetsu and Enma. These blades are all highly rated swords and, with Zoro's Haki, he can cut through most things. Zoro is a strong character and one day he will achieve his dream of becoming the world's strongest swordsman.
10 ADMIRAL FUJITORA (CAN'T)
Issho is a very powerful swordsman and a user of the Zushi-Zushi no Mi, which turned him into a gravity manipulating swordsman. Fujitora has used this technique against Zoro before and it did pin him down. In fact, it created a crater in Dressrosa. Zoro did manage to escape it though. Zoro would definetly put up a solid fight and, with his new sword, Enma, he might even stand a chance of grabbing a victory. However, Fujitora is the stronger overall fighter at this moment in the story. Zoro will one day surpass him, but he has not done that yet.
9 MONET (CAN)
Monet was an officer in the Donquixote Family and the previous owner of the Snow-Snow fruit. With that ability, she can quickly turn her surroundings into a winter nightmare. As a logia, she is also invulnerable to most attacks. Despite these things, she was easily defeated by Roronoa Zoro in the Punk Hazard arc. Zoro approached Monet head-on and used his Great Dragon Shock. Zoro didn't use Armament Haki, but still managed to do damage to Monet. She was so scared of him that, once she'd been cut, she couldn't reform her body like a normal logia user would.
8 RAYLEIGH (CAN'T)
"Dark King" Silvers Rayleigh was once right hand man to the pirate king, Gol D Roger. At that time, Rayleigh was regarded as one of the strongest men on the planet. He's since retired from piracy and, though he is weaker now, he is still incredibly strong. Before the time-skip, Rayleigh fought on equal terms against Admiral Kizaru, a logia user and one of the strongest marines. Kizaru even mentioned that he would need to make preparations beforehand if he wanted to capture Rayleigh. During his time in Roger's crew, Rayleigh was one of the strongest swordsmen in the world and, even though he's gotten weaker at this point, he is still stronger than Zoro.
7 HODY JONES (CAN)
Hody Jones is currently a prisoner, having once led the New Fish-Man Pirates in an attempt to take over all of Fish-Man Island. Hody is a follower of the ways of Arlong. This means, he believes fish-men are superior to humans. As such, he is of the belief that fish-men should rule and do whatever they want with humans. He fought against Zoro in the Fish-Man Island arc and, though they were underwater, Zoro was able to beat him using his One Sword Style Technique: Death-Lion's Song.
6 KAIDO (CAN'T)
Emperor of the Sea and the strongest creature in the world, Kaido, is believed to be the strongest pirate alive. Legend says that Kaido is "unkillable" and his scales are believed to be impenetrable. It is believed that there isn't a single person in the world that could beat Kaido in a one one one fight. That's how strong this pirate is. He consumed a devil fruit that gives him the ability to transform into an Eastern Dragon and, in this form, he can blast through mountains with his dragon breath. Zoro's sword, Enma is the only weapon known to have wounded Kaido, meaning, he might be able to deal damage to the Yonko, but it is still too soon for him to defeat him.
5 PICA (CAN)
Former officer of the Donquixote Family, Pica is a pirate that consumed the Stone-Stone fruit and, with its power, he made a name for himself. Pica's fruit allows him to control, turn into and create large amounts of stone, which means he can launch city-sized attacks. Despite this, Zoro was easily able to cut through these large chunks of stone before getting to Pica's real body. In their final confrontation, Pica clads himself in Armament Haki and Zoro clads his swords and they launch themselves at each other. Zoro cut through Pica's reinforced skin using his serect technique, Three Thousand Worlds.
4 SHANKS (CAN'T)
Red Hair Shanks has been a Yonko for the last 6 years in the One Piece world. In that time, he and his crew has earned the respect of some of the strongest men on the sea. Shanks has wonderful pedigree, having been a member of the pirate king, Gol D Roger's crew. Even though he was young, Shanks traveled with Roger to the end of the Grandline and, to do this, he needed to be strong. He's only grown in strength and used to duel on even ground with Dracule Mihawk. Since then, Shanks lost his arm, but he is still superior to most pirates, including Zoro.
3 KAKU (CAN)
Kaku is a member of the World Government's secret organization, Cipher Pol Aigis Zero. This is an organization dedicated to carrying out the will of the Celestial Dragon's and Gorosei in a covert manner. Kaku is a strong swordsman and former member of Cipher Pol Nine, where he went up against Zoro and lost. At the Judicial Island, Enies Lobby, Zoro and Kaku did battle in a building that was falling apart. Zoro dug in deep and used his Nine Sword Style Technique Asura: One Mist Silver to win the fight. Zoro has grown immensely since then and would still be able to beat a stronger version of Kaku.
2 DRACULE MIHAWK (CAN'T)
Dracule Mihawk is the strongest swordsman in the world. It is not known when exactly Mihawk achieved this title, but he's lauded as one of the strongest men on the seas. Mihawk is a former Warlord of the Sea, known for his relaxed and reserved demeanor. Despite being a fairly calm man, Mihawk always yearns for great battles, like where we him go up against the future Yonko, "Red Hair" Shanks. The last time Zoro and Mihawk dueled, he was easily outclassed and, since then, Zoro has grown immensely. Despite this growth, it is still too early for Zoro defeat Mihawk and become the world's strongest swordsman.
1 DAZ BONEZ (CAN)
Daz Bonez is a former member of the criminal organization, Baroque Works. In his time as an operative, he was the second strongest member behind the former Warlord, Crocodile. Daz was known by the marines to be a masterful assassin who strikes with deadly force and precision. With his Dice-Dice fruit, he could effortlessly slice through buildings, making him a tough opponent. Daz played a massive role in Zoro's development, as it is in this battle that Zoro learns to cut steel. Zoro does that and defeats Daz and has since risen even further since the Straw Hats have entered the New World. Zoro is a man destined to be the strongest swordsman, meaning, he is out of Daz Bonez league.