Abstract: We studied the change of the antioxidant system of Prorocentrum donghaiense during lysing process treated with Halomona Sp.DH-e cell-free filtrate and the acute toxicity test of fermentation products to explore the inhibitory mechanism of DH-e on the P.donghaiense and acute toxicity of DH-e fermentation products.The results showed that the reactive oxygen species (ROS) metabolism of algae cell had an increasing trend after treated with DH-e aseptic filtrate.Then the self-protection mechanism of algal cells was started.Furthermore, of the activities of antioxidant enzymes, such as superoxide dismutase (SOD) and catalase (CAT), and Malodialdehyde (MDA) content both were increased.We found that the semi-lethal concentration was LC₅₀ > 1 00 mg/L when the zebrafish treated with fermentation products for 96h.The mortality rate of zebrafish effected by fermentation maximum dose (5 000 mg/kg·bw) was 0% in 14 d (LD₅₀ > 5 000 mg/kg·bw).These results revealed that the fermentation is low-toxic.