The impact of dietary alpha-tocopherol on juvenile Chinese mitten crab Eriocheir sinensis was experimentally evaluated in a 10-week study. Crab were fed with nine diets including three levels of alpha-tocopherol (0, 100 and 300 mg kg-1 diet) and three levels of fish oil oxidation (fresh, moderate and high) in triplicates. Fresh and moderate oil oxidization enhanced weight gain, but moderate and high oil oxidization lowered survival and feed efficiency. The 100-mg alpha-tocopherol kg-1 diet resulted in higher hepatopancreas MDA than other alpha-tocopherol diets. High oil oxidization led to the lowest serum superoxide dismutase (SOD) and glutathione peroxidase (GPH-PX). The serum SOD and GPH-PX activities in crab fed 100 mg alpha-tocopherol were higher than in those fed other alpha-tocopherol diets. The diet without alpha-tocopherol addition lowered lysozyme and phenoloxidase (PO) activities compared to other alpha-tocopherol diets. Fresh fish oil diet increased PO activity compared to oxidized oils. High oil oxidization caused significantly more mortality than fresh or moderate oxidization after 7-d postchallenge with Aeromonas hydrophila. Supplementation with alpha-tocopherol significantly enhanced resistance to bacterial infection. This study indicates that alpha-tocopherol can protect lipid from peroxidation and enhance disease resistance.