Objective：To explore the embryo tolerance of endotoxin and the solution to embryo contamination by discussing the effect of endotoxin and escherichia coli reproduction on the development of mouse embryos in vitro. Methods：Totally 150 mouse 2-cell embryos were randomly assigned into five groups，named groups A to E. A was control group；endotoxin was added to microdroplet of groups B and C at 0.25 EU/ml，0.5E U/ml；groups D and E were polluted by escherichia coli while culture media of group E was re－placed after 24 h. To evaluate the quality of embryos，the development of embryos on the first day（D2） and the third day（D4）in dif－ferent groups was observed. Results：The development rate and blastocyst rate were 100% in control group as well as in groups B and C without significant differences. On D2，the survival rates were not significantly different between groups D and E（P>0.05），but on D4，the blastocyst rate in group E was significantly higher than that in group D. Conclusion：Bacteria breeding exerts greater toxic ef－fect on embryo development than endotoxin. Stopping contamination in time can improve the result of embryo development. Low dose of endotoxin has no effect on mouse embryos in vitro.