Introduction: Mammalian embryos as well as oocytes are prone to various doses of visible light during manipulations in laboratory. The present study was designed to investigate the effects of visible light on the development of mouse 2- cell embryos. Method: Non-pregnant female NMRI mice were super-ovulated with i.p. injection of 7.5 iu PMSG followed 48 hours later with 10 iu hCG. Forty eight hours after mating, the uterine tubes were removed and 2-cell embryos were transferred into HTF medium by flushing method. Morphologically normal embryos were collected and exposed to 1600 Lux light for 30 minutes. Every 10 minutes a number of embryos were allocated into either HTF or MEM-α medium. Treated embryos as well as controls were incubated at 37°C with 5% CO2 in air. Developmental stage of embryos was recorded every 24 hours for 5 days. Experiments were replicated 8 times and data were analyzed with χ 2 test. Results: In the treatment group, the development of embryos that underwent 30 min. exposure to visible light was significantly lower (27% and 21% in HTF and MEM-α media respectively) compared with control group (49% and 52% in HTF and MEM-α media respectively). Development of embryos that underwent 10 and 20 min exposure to visible light was lower than controls but the difference was not statistically significant. Percentage of development in HTF and MEM-α was nearly identical. Conclusion: It can be concluded that mouse 2-cell embryos are not able to withstand the deleterious effects of visible light when the time of exposure exceeds 20 min. However, lower doses of visible light may be tolerated particularly when simple media such as HTF are used.