Objective:To measure the levels of reactive oxygen species (ROS) at each development stage of early embryos incubated with glucose in vitro,and to probe into the mechanism by which glucose blocks the development of mouse early embryos.Methods: Mouse early embryos were cultured with different concentrations of glucose （0,5,10,15,20,25 and 30 mmol/L） added in modified CZB (m-CZB) medium.ROS levels inside and outside of embryos were examined by molecule probes of hydroethidine and spectrophotometry at different stages of embryos.Results: When glucose concentration reached 15 mmol/L,the blastocyst developmental rates decreased significantly compared with control (0 mmol/L glucose,P<0.05); superoxide anion (O2-·) levels inside embryos and hydrogen peroxide (H2O2 ) levels in the medium with 15 mmol/L glucose were significantly higher (P<0.05) than those in medium with no glucose at late 2-cell stage.However,there was no significant difference in O2-·levels in the embryos exposed to 15 mmol/L glucose and no glucose at other growth stages (P>0.05).Conclusion: High glucose may induce ROS production at late 2-cell stage and block the development of mouse embryos.