To evaluate the aneugenic effects of carbendazim (MBC) and griseofulvin (GF) on meiosis, we cultured mouse oocytes, allowing them to mature in vitro in the presence of MBC and GF. The incidence of hyperploidy was significantly increased in oocytes cultured with 0.6 μg/mL or higher concentration of MBC, while the incidence of diploidy was significantly increased in oocytes cultured with 1 or 3 μg/mL of GF. To investigate the stage-specific effects of these chemicals during meiotic progression, the oocytes were exposed to chemicals for the initial 7 h or final 8 h of the culture. Both MBC and GF were found to effectively induce numerical aberration during the final half of the culture. Thus, in vitro maturation of mouse oocytes is a useful model for the detection of chemically induced aneuploidy and for the detection of stage-specific effects of chemicals during meiosis.