The present invention relates to a method for determining a genotoxicity of a test substance, comprising the steps of: (a) transforming a fish with a nucleotide sequence encoding a non-fluorescent fluorescence protein with a mutation; (b) treating a test substance to the transformed fish; and (c) measuring a fluorescence in the test substance-treated fish, wherein the fluorescence is generated by reversion of the non-fluorescent fluorescence protein to the fluorescence protein due to a back mutation of the nucleotide sequence in the test substance-treated fish. According to the present invention, MutaFish system, Zebrafish (Brachydanio rerio) line, in which the fluorescence protein variant, preferably wild type EGFP variant (EGFPmut) is transformed, provides a much excellent animal system for measuring a genotoxicity of a test substance via production of a fluorescent fry larvae generated through reversion of the fluorescent protein variant caused by treatment of the test substance. Accordingly, the MutaFish system of the present invention may determine a genotoxicity of a test substance in much more simple and high-throughput manner in an eukaryote to which the conventional methods (e.g., Ames test) may be not applied.