BACKGROUND: All-trans retinol is a biological antioxidantscavenging the ROS in the cell culture. OBJECTIVES: This studywas conducted to investigate the effect of all-trans retinol infertilization and culture medium on mouse embryo's developmentalcompetence. METHODS: This study was designed into twoexperiments. In the first experiment, in vitro mature oocytes wereco-cultured with sperm in fertilization medium containing differentconcentrations of all-trans retinol (0, 1, 5, and 10 μM). Afterfertilization, zygotes in each group were separately cultured in CZBculture medium for 5 days to the blastocyst stage. In the secondexperiment, in vitro produced zygotes were cultured in CZB culturemedium containing different concentrations of all-trans retinol (0,1, 5, and 10 μM) for 5 days to the blastocyst stage. RESULTS: In thefirst experiment, the blastocyst formation rate significantlyincreased by 5 μM in all-trans retinol, which was more than those ofthe other groups. Also, percentage of grade one embryos wassignificantly higher in the presence of 5 μM all-trans retinol thanthose in the presence of 0 and 1 μM all-trans retinol. In the secondexperiment, different concentrations of all-trans retinol could notalter blastocyst formation rate; however, the percentage of gradeone embryo was higher in the presence of 10 μM all-trans retinolthan that of the control group. CONCLUSIONS: These resultsshowed that supplementation of fertilization medium with 5 μM alltransretinol could improve mouse embryo's development andmorphology. On the other hand, supplementation of embryo culturemedium can improve mouse embryo morphology without anyeffect on embryo developmental competence.