Objective To establish gestational diabetes mellitus model with macrosomia in rats Methods\ 7 days after being injected STZ 25mg/kg intraperitoneally,Female SD rats were mated with the male.On the day 6 of conception,plasma glucose(PG) levels were determined and those whose PG level increased by 20% than that before pregnancy were selected as the Model(M) group.All rats were c-sectioned on the day 21 of pregnancy to observe the fetuses.Results\ Body weights,body lengths,tail lengths of the offspring in M group were significantly heavier or longer than those in C group(P<0.001).Fetal plasma glucose concentrations in M group were higher than those in C group and the statistic difference was noted(P<0.001).Conclusion\ 7 days after being injected STZ 25 mg/kg intraperitoneally,GDM rats with 20% increase of plasma glucose levels on the day 6 of conception than before pregnancy can produce macrosomia.