Research of antioxidant activity of syrup purple sweet potatoes (Ipomoea batatas L.) had been done. The research conducted in Agriculture Laboratory of University of Quality and Laboratory of Pharmacy, University of North Sumatra, for three months, October-December 2014. Propose of the research is to know whether the temperature of liquidation has impact to degree of anthocyanin syrup of purple sweet potatoes. Testing of antioxidants activity is using DPPH method. Results of the research shown, liquidation temperatures has significantly effects to decline the degree of anthocyanin. Degree of anthocyanin in liquidation temperature of 80°C is 112.310 mg/100 g, in liquidation temperature of 95°C is 108.806 mg/100 g, and in liquidation temperature of 110°C is 107.876 mg/100 g. Antioxidant activities of syrup is decline when liquidation temperatures is escalation. Values of IC 50 in each of syrups are S1 (liquidation temperature 80°C = 129.87 mg/ml); S2 (liquidation temperature 95°C = 109.16 mg/ml); and S2 (liquidation temperature 110°C =55.29 mg/ml).