Abstract: Effects of Aureococcus anophagefferens on superoxide dismutase (SOD) activity, malondialdehyde (MDA) and glutathione (GSH) contents of mussel Perna viridis were studied by feeding P. viridis with pure culturing A. anophagefferens and co-occurring algae (A. anophagefferens and Tetraselmis subcordiformis). Mussels fed with T. subcordiformis were set as control. The results showed that A. anophagefferens significantly effected the antioxidant enzyme system in mussel P. viridis including SOD, MDA, and GSH. SOD activity and MDA, GSH contents fluctuated after P. viridis exposing to A. anophagefferens. The high and moderate cell densities of A. anophagefferens can affect the SOD activity significantly within a short time (3 h). SOD activity in the mussel exposing to the co-occurring algae, by contrast, increased slowly, suggesting that T. subcordiformis can prolong reaction time of the antioxidant system. Compared with control group, GSH content in each experiment group was significantly reduced in 2 d. GSH contents had no difference in the mussel exposed to co-occurring algae and pure culturing A. anophagefferens, which suggested that T. subcordiformis has no positive effect on restoration of the antioxidant system in mussels.