Abstract: In this study, the acute toxic effects of the water-soluble fraction of crude and fuel oil with or without dispersants were investigated, using chlamys farreri and apostichopus japonicus as test organisms.The 96h-LC₅₀ values for chlamys farreri and apostichopus japonicus were resulted:fuel oil with dispersants (1.14 mg/L, 0.16 mg/L) > crude oil with dispersants (1.39 mg/L, 0.74 mg/L) >fuel oil without dispersants (1.80 mg/L, 4.10 mg/L) > crude oil without dispersants (3.40 mg/L, 6.44 mg/L).It is showed that the test substances had significant toxicity on the chlamys farreri and the apostichopus japonicas:the toxicity of the light oil(fuel oil) is higher than that of the heavy oil(crude oil) and the oil dispersants could make the toxicity much more higher, especially for apostichopus japonicus.The results also indicated that chlamys farreri and apostichopus japonicus were the proper test organisms for ecological risk assessment of marine oil spills.