Zinc is a vital nutrient in the normal reproductive function and embryonic development of mammals, and it is well known that oyster extract contains significant amounts of zinc. The effects of oyster extract on reproductive function, such as embryonic development, serum levels of zinc and sperm maturation were examined in zinc-deficient mice. Zinc deficiency in dams during pregnancy induced a decrease in the successful pregnancy rate, maternal weight gain, the number of live fetuses and fetal body weight. Zinc deficiency for 12 weeks in male mice induced a decrease in body weight, testis weight and sperm count in the epididymis. However, reproductive failure, embryonic defects and decreased sperm motility in zinc-deficient mice were improved by supplementation with oyster extract. Some nutrients contained in oyster extract, such as taurine and glycogen, may be related to the recovery of reproductive function. There were significantly lower serum concentrations of zinc in dams fed a zinc-deficient diet. However, the serum zinc concentration was normal in the oyster extract-supplemented group. No difference in the concentration of serum zinc was observed between the oyster extract- and zinc carbonate-supplemented groups. From these findings, it is suggested that oyster extract is a useful supplement that can prevent reproductive defects from zinc deficiency, and the bioavailability of zinc may be identical to zinc carbonate.