This study evaluates the effects of a microwave and steam cooking combination on the sugar composition, phytochemical compounds (total phenolics, total flavonoids, total anthocyanins and phenolic acids and anthocyanin compositions) and antioxidant capacity of purple sweet potatoes (PSPs). The combination of microwave and steam cooking could significantly decrease the cooking time. The results show an obvious increase in the quantity of total phenolics, flavonoids, and anthocyanins in PSPs after cooking. The microwave and steam cooking combination induced the greatest increase for the total flavonoids and total phenolics, with values of 22.2% and 26%, respectively. Among the phenolic acids in the PSP extract, chlorogenic acid was the major constituent, and phenolic acid concentrations increased after cooking, except for caffeic acid. An HPLC-MS analysis of anthocyanin showed that the cyanidin-3-(6"-caffeoyl-6"'-feruloylsophoroside) -5-glucoside and peonidin-3-(6"-caffeoyl-6"'-feruloylsophoroside)-5-glucoside contents in PSPs cooked with steaming for 10 min followed by microwaving for 3 min (S 10 _ M 3 ) were highest among the cyanidin and peonidin compounds. The PSPs exhibited a greater antioxidant capacity after cooking, and the S 10 _ M 3 cooking method produced the greatest antioxidant capacity. Therefore, an appropriate combination of microwave and steam cooking can better retain phytochemical compounds in PSPs and increase antioxidant capacity compared with only steaming or microwaving.Keywords: purple sweet potato, microwave, steaming, phytochemical compounds, antioxidant activity flavonoids and phenolic compounds (Blessington et al., 2010;Giusti et al., 2014;Tierno et al., 2015). Previous studies have shown that purple sweet potatoes (PSPs) exhibit strong antioxidant activity and an anti-mutagenic capacity, and they clearly decrease high blood pressure and liver injury (Kim et al., 2015;Truong et al., 2012). Considerable research on PSP has quantified the antioxidant activity as well as phenolic acid and anthocyanin compositions for various cultivars or after different cooking treatments (Kita et al., 2013;Lemos et al., 2015;Perla et al., 2012). A study performed by Lemos et al. (2015) showed the total phenolic and anthocyanin quantities as well as antioxidant activity in potatoes increased after steaming and microwaving. In addition, baking, frying and microwaving increase antioxidants as well as the carotenoid and total phenolic content in potato according to Blessington et al. (2010). However, Perla et al. (2012) reported that the total phenolics, flavonoids, anthocyanins and antioxidant activity in potatoes were significantly reduced by a microwave treatment.