Cadmium (Cd) is the most common heavy metal and is easily detected in aquatic environments on a global scale. Vitamin C was a widely used vitamin in aquaculture. The aim of this study was to explore the potential of vitamin C in ameliorating Cd-induced toxicity in grass carp kidney (CIK) cells. Cell viability, oxidative response, metallothionein (MT), and immune-related gene expression was analyzed in the present study. The results show that cell viability was significantly reduced following Cd exposure, but the vitamin C supplementation attenuated the increased in cell viability. In addition, vitamin C supplementation can increase the antioxidation response and MT and immune-related gene expression. These results indicate that vitamin C has the potential to alleviate the effects of Cd toxicity in CIK cells.