The aim of this study were to determine phenolic content and antioxidant activity of three varieties of banggai sweet. Research methods used the complete random methods on banggai sweet potato varieties of purple sweet potato, yellow sweet potato and white sweet potato with 5 times replication and to obtain 15 experiment units. The influence of ethanol ratio of banggai sweet potato flour and extraction time treatment produced extract phenolic content and influence varieties of banggai sweet potato phenolic content and activity of antioxidant applied to achieve the aim. The results shown that highest phenolic content (2,63%) was white banggai sweet potato, 2,44% of purple banggai sweet potato and 1,90% of yellow banggai sweet potato at ratio 15 : 1 based volume/weight (v/w) and time extraction at 2 hours. The highest activity of antioxidant ethanol extract (74,87%) was found at white banggai sweet potato extract and lowest activity of antioxidant (37,19%) was found at yellow banggai sweet potato. Antioxidant activity had relations with phenolic content. Antioxidant activity of 200 ppm BHT as control had no significant different with antioxidant activity of white sweet potato ekstract.