A study was conducted on the effects of cultivar, size and method of cooking on quality attributes and nutrient content of sweet potatoes. The sweet potatoes were cooked by baking, boiling, steaming, microwave and canning, and subsequently analyzed. Sensory evaluations were also conducted. Ascorbic acid, riboflavin and carotenoids were highest in the cultivar Centennial and lowest in Georgia Jet. Niacin content was higher in Jasper than the other cultivars, while Goldrush and Centennial contained more pantothenic acid. Large roots contained more ascorbic acid and carotenoids, but B‐vitamins did not vary with size. Canned roots were lower in all vitamins tested, except for carotenoids. Baking retained more of the vitamins, followed by microwave cooking. Generally, baking and microwave cooking produced better color, higher total solids and better flavor. Microwave cooking resulted in less moistness and smoothness. Cultivars and sizes responded differently to cooking, thus producing significant interactions. Copyright © 1979, Wiley Blackwell. All rights reserved