To investigate the effects of octylphenol and nonylphenol on the reproduction of the striped field mouse, the mice were subcutaneousely injected with 4-t-octylphenol 800 mg/kg (OP800), nonylphenol 900 mg/kg (NP900) or OP800 + NP900 (OPNP), respectively, in two times a week for 2 months. As the results, there were no differences between the control and the compound-treated groups in the body weight in both sexes, and the GSI (gonadosomatic index) and SVI (seminal vesicles index) in the adult males. But histological abnormalities of the reproductive organs in the mice seems to be related to the compound. This suggestion is supported by the facts that most mice treated with the compounds had only a small number of spermatozoa in the shrunken epididymal tubules. In addition, the shrunken reproductive organ in one mouse treated with the NP, suggests that the abnormalities in the wild striped field mice might be induced by the compound. Furthermore, it is indicated that the compounds must be toxicants to inhibit pregnancy, judging from the fact that all the mice treated with the compounds had failed to deliver.