Abstract: There is little information about the influence of organic solvents for low water-solubility organic compounds on Photobacterium phosphoreum toxicity test, though it appears likely that much of data were obtained by using solutions prepared with cosolvents or surfactants.In this study the influence of five stock solvents, including dimethyl sulphoxide (DMSO), acetone, aether, ethanol, tetrahydrofuran, on Photobacteriumphosphoreumtoxicity test was measured and different effective concentration values were obtained.DMSO was selected as the most suitable solvent for organic compounds with low water-solubility according to its good characteristics and less toxicity effect on Photobacterium phospherum.Chlorobenzene and nitrobenzene with proper solubility were selected to verify the effect of DMSO on Photobacteriumphosphoreum toxicity.It was demonstrated that DMSO (concentration no higher than 0.20 mol•L^-1) had little effect on the toxicity of organic chemicals with relative error no more than 10%.The successful application of DMSO as cosolvent provided a good example and a good idea to improve traditional acute toxicity test of Photobacterium phosphoreum, and broadened the application to identifying the toxicity of low water-solubility organic compounds.