Methyl tertiary-butyl ether(MTBE), a new gasoline additive, is added to gasoline as an octane enhancer and used to reduce automotive emissions. Using Ames test, unscheduled DNA synthesis (UDS) assay and cell micronucleus test, the authors evaluated the genotoxicity of domestic produced MTBE. MTBE did not show any mutagenic potential in Ames assay(TA98, TA100 strains) with or without rat liver-derived metabolic activation system (S-9). Rat primary hepatocyte UDS assay showed that MTBE could damage DNA. In NIH3T3 cell micronucleus test, MTBE showed negative results. It could be concluded that MTBE has some genotoxicity at DNA level.