Abstract: Objective: Observe the cytotoxic effects of argon laser photocoagulationsa on cattle pigment epithelium cells and the protection effect of dexamethsone (Dex) to the RPE cells. Methods: Different power of argon lasers were used to coagulated confluent RPE cells, then the cell killing rates (CKR) were study by MTT assay. we have observed the killing rate of 0.8 W laser after or before use three different concentration Dex also. Results: Different power of lasers have variable CKRs. The CKRs have a line relationship with the laser powers. The use of Dex before laser coagulation could alleviate the effect of laser, but after laser coagulation had no use.Conclusion:The CKRs of laser has positive correlation with its output power. Using Dex before laser coagulation can protect the RPE cells from being killed partly.