We previously reported that 2-cell embryos obtained after administering cadmium (Cd) to mice immediately before ovulation already demonstrated reduced developmental ability. To determine when this Cd toxicity appears in mouse oocytes before the 2-cell stage, we exposed oocytes to Cd at maturation and during the fertilization period using IVM and IVF techniques. Four experimental groups were defined by the period of Cd exposure: IVM group, exposure at the maturation period; IVF group, exposure at the fertilization period; IVM · IVF group, exposure during both periods; Control group, no exposure. Oocytes obtained from the ovaries were subjected to IVM and IVF, and the fertilization and developmental rates were investigated in all groups. As a result, Cd exposure during the maturation period disturbed fertilization of oocytes, and Cd exposure during the fertilization period disrupted the normal development of embryos after fertilization. This suggested that the manifestation of Cd toxicity in oocytes clearly differed with the exposure period. In addition, it was shown that Cd exposure during the maturation or fertilization period influenced the early development (including the fertilization) at a lower concentration than exposure after the 2-cell stage.