The Sandai Kitetsu is one of the Wazamono grade swords, a 'Sharp Sword'. Like all of its predecessor Kitetsu swords, this one is said to be cursed.
Zoro picked the sword from a barrel of cheap katanas in a shop at Loguetown after sensing its quality; Tashigi later identifies the sword from a catalogue. When the owner first saw it, he was not going to allow Zoro to buy it, telling him of the curse. Zoro liked the concept and decided to test his luck against the curse. He threw it into the air and held out his arm, willing to let it cut his arm off. Zoro's luck won and the blade circled neatly around his arm. The shop owner gave Zoro both Sandai Kitetsu and Yubashiri for his skill and luck.