AIM:To investigate the operation effects of using different concentration mitomycin C(MMC) intraoperatively on laser epithelium keratectomileusis(LASEK). METHODS:Totally 261 patients 496 eyes were devided into two groups:group 0.4mg/mL MMC(133 patients,245 eyes);group 0.2mg/mL MMC(128 patients,251 eyes). 0.4mg/mL and 0.2mg/mL MMC sulution were intraoperatively applied to the cases respectively.The two kinds of instilled solutions were held up in the eyes for 30,60,90 and 110 seconds successively according to the≤-3.00, -3.25- -6.00,-6.25～-9.00,≥-9.25 of diopter.The formation of corneal haze,the situation of visual acuity, the change of diopter,corneal endothelium density,the healing of cornea were observed. RESULTS:All the patients were followed up for 1 year. The clinical data of group 0.4mg/mL MMC and group 0.2mg/mL MMC were respectively as follows:the occurrence rate of haze was 1.2%and 13.2%;the appearance rate of influenced visual acuity was 0.8%and 2.0%;the changes of diopter were -0.52±0.09 and -0.67±0.11D(1 month),-0.29±0.15 and -0.58±0.21D(6 months),-0.35±0.16 and -0.54±0.18D(12 months);the corneal endothelium density of the two groups prooperation, 1 month,4 and 12 months after operation respectively was 2994.01±321.89 and 3005.92±382.54, 2974.89±339.87 and 2996.69±374.19,3001.02±306.92 and 2988.37±367.33,3011.18±321.31 and 3000.05±299.84. There was a statistically significant difference(P<0.05) in those index.But there were respectively two cases(3 eyes) and two cases(2 eyes) of Filamentary keratitis after taking off lenses in group 0.4mg/mL MMC and group 0.2mg/mL MMC. CONCLUSION:Using 0.4mg/mL MMC solution intraopera-tively can effectively inhibit haze formation and there for improve the results of LASEK greatly,and it is better than 0.2mg/mL MMC.