Objective : To investigate the effects of 3 types of trihalomethanes ( THMs) , the by⁃products in treatment of drinking water disinfection , on the development and reproductive capacity of germ cells of Caenorhabditis elegans. Methods : Tribromomethane ( TBM) , trichloromethane ( TCM) and triiodomethane ( TIM) , 3 types of THMs were selected and wild type Caenorhabditis elegans was used as a model to detect germ cell apoptosis , oocyte number and the final brood size after exposure to different concentrations of THMs. Results : The results of germ cell apoptosis showed that the exposure to 50 μmol/L TCM and TIM caused elevated levels of germ cell apoptosis in a dose⁃dependent manner. Oocyte counting results showed that exposure to 50 μmol/L all three THMs significantly reduced the number of oocytes. The brood size results showed that only 50 μmol/L TIM exposure significantly de⁃ creased the brood size of nematodes. Conclusion THMs showed negative impacts on the reproductive system of Caenorhabditis elegans , and the toxicity is related to the halogenated elements of THMs.