This study aimed to determine the effects of dietary supplementation with vitamin C (l-ascorbic acid, AsA) on lead (Pb) accumulation and toxicity in sea cucumber, Apostichopus japonicus. Three hundred sea cucumbers (10.02±0.02g) fed a basal diet containing 100mg Pb/kg were subjected to 5 levels of l-ascorbate-2-polyphosphate (LAPP) supplementation to achieve 5 AsA treatment levels of 0, 2727, 4630, 9171, 13,893mg AsA/kg. After 30 days, specific growth rate (SGR) and body weight gain (BWG) of supplementation groups were significantly (P<0.05) higher than the control group. Pb contents of the intestine significantly (P<0.05) decreased from 20 days to 30 days in all supplementation groups. Pb contents of the respiratory tree in sea cucumbers in the 2727 and 4630mg AsA/kg treatment groups significantly (P<0.05) decreased from 10 days to 30 days. Superoxide dismutase (SOD) activity, glutathione peroxidase (GSH-Px) activity and total antioxidant capacity (T-AOC) of the sea cucumber body wall in supplementation groups increased after 30 days. Malondialdehyde (MDA) content of the body wall significantly (P<0.05) declined with increasing AsA level. Therefore, it can be demonstrated that vitamin C could mitigate the effects of Pb on sea cucumber and the optimum levels ranged from 2727mg AsA/kg to 4630mg AsA/kg when Pb levels were 100mg/kg.