Abstract: Melamine had become the focus of feed safety assessment because of the tainted pet food and milk powder scandal happened in 2007 and 20081Melamine is a high nitrogen content industrial chemicalmaterial, but it was falsely added to protein sources to enhance the apparent p rotein content for the bigger profit. In this study, the acute toxic experiments(including touching test, injection test and oral test) were conducted on Japanese sea bass(Lateolabrax japonicus) to assess the safety of melamine in fish. In touching test, Japanese sea bass(50g±011g) were exposed to 0 and 3500mg/L melamine solution at 27℃ for 96h, no feed was provided to the experimental fish during trial, the mortality of the Japanese sea bass were calculated after 96h; In injection test, the melamine was injected into Japanese sea bass(75g±111g) at 0, 200, 360, 648, 116614 and 2099152 mg/kg·w levels from the abdomen, respectively, lasted for 14d in a recirculation rearing system, and the fish were fed once daily, the mortality of Japanese sea bass were calculated after 14d, LD50 and the confidence limitation of LD50 95% were calculated using Korbormethod; In oral test, the effects ofmelamine in feeds on the feed intake, growth performance, serum parameters of Japanese sea bass were investigated.The concentrations of melamine in experimental diets were 0, 500, 2000, 5000 and 10000 mg/kg respectively, each diet was fed to trip licate group s of the experimental fish, the initial body weight of Japanese sea basswas 30.58±0105g, fish were reared in a rearing system for 21d. The results showed that the solubility ofmelamine was low and the LC50 was beyond 3500 mg/L at 27 ℃ in touching test.The LD50 of Japanese sea bass in injection test was 890107mg/kg·w, and the confidence limitation of LD50 95% was 778163-1017145 mg/kg·w. In oral test, the feeding intake and growth performance were significantly decreased and the feed conversion ratio was significantly increased in 10000mg/kg melamine treatment(ppp> 0105).The 21d NOAEL(no2observed2adverse2effect2level) for melamine in Japanese sea bass was 131199 mg/kg·w·d. In conclusion, no acute toxicitywas observed formelamine solution in Japanese sea bass; the LD50 in injection testwas 890107 mg/kg·w and the confidence limitation of LD50 95% was 778163-1017145 mg/kg·w; The melamine in feed had significantly decreased the feeding rate and growth performance in Japanese sea bass, the 21d NOAEL formelamine in Japanese sea bass was 131199mg/kg·w·d.