Purple, red and yellow flesh sweet potatoes were evaluated to compare their in vitro antioxidant capacity. The results show that the total polyphenols, reducing power, scavenging DPPH radical activity and superoxide dismutase activity of purple flesh sweet potato is far superior to red and yellow flesh sweet potatoes. Purple flesh sweet potato is abundant of polyphenol, and showed the higher antioxidant activity than red and yellow flesh sweet potatoes.