As the commander of the 3rd division of the Whitebeard Pirates, Jozu has authority over the lower-ranking subordinates. During the Marineford war, Jozu was powerful enough to fight on par against the Shichibukai and Marine admirals.
Jozu has outstanding brute strength, comparable to that of the Giant Squad Marines, if not greater. He picked up and hurled an immense iceberg at a great distance at the giants protecting Marineford. The iceberg was so enormous that it was at least ten times as big as any of the Giant Squad’s members. Thus, Jozu has demonstrated one of the greatest feats of strength seen in the series, though it is currently unknown how losing his right arm will affect his strength.
Jozu has eaten the Kira Kira no Mi, a Paramecia-type Devil Fruit which allows him to transform parts and most likely all of his body, into diamond. This power has earned him the nickname “Diamond Jozu”.
It can be mistaken for a Logia-type due to the fact that he can willingly transform his entire body into an element, something that distinguishes Logia users from Paramecia users; but it is a Paramecia-type due to the fact he did not reform his arm after it was severed. He also has not been seen producing diamond outside the perimeter of his body, which is one of the common characteristics of Logia-users. This implies that it could be a fruit that grants the user the power to encase himself rather than transforming.
Jozu’s powers give him the ability to greatly increase his offensive and defensive capabilities, as his already strong physical attacks are enhanced by the density of his diamond body. His defenses seem to enhance exponentially, and he is able to block the strongest slash in the world from the world’s greatest swordsman, Shichibukai Dracule Mihawk with no visible damage to himself, as diamond is one of the hardest substance in the world, along with Seastone and the Poneglyphs.
Despite his massive body, his speed and reflexes are on par with his brute force. This speed, combined with his Busoshoku Haki, makes Jozu (especially when he’s in his Diamond form) particularly dangerous against Logia users; He launched a devastating surprise attack against Crocodile that knocked him a great distance back.
Later, he launched another surprise attack against Admiral Aokiji, which shattered his ice form and caused the Admiral to bleed from the mouth.