AIM:To investigate the preoperative relative factors for night glare after LASIK for myopia. METHODS:A total of 665 cases(1257 eyes) with myopia were divided into 2 groups:group Ⅰ(low and moderate myopia) -1.00~-6.00D,group Ⅱ (high myopia) -6.25~ -14.25D. Pupil sizes during scotopic conditions were measured before surgery using ObscanⅡ. All cases underwent standard LASIK. The cases were observed postoperatively 3 months. The self-perceived night glare of each eye was investigated. The relative factors of night glare such as preoperative scotopic pupil sizes and attempted correction of spherical equivalent were analyzed. RESULTS:The scotopic pupil sizes in low,moderate myopia group were 6.81±0.50mm,and that in high myopia group was 6.98±0.57mm. There was significant difference in the scotopic pupil sizes between the two groups(P=0.001). The night glare in low,moderate myopia group was complained by 58 eyes (7.9%),and that in high myopia group was complained by 137 eyes (26.2%). There was significant difference in the night glare between the myopia of degrees(P=0.000). There were significant differences in pupil size and attempted correction of spherical equivalent betweens eyes with night glare and without night glare in high myopia group (P=0.001,0.002,respectively),and there were significant differences in pupil size,and there were no significant difference in attempted correction of spherical equivalent in low,moderate myopia group(P=0.000,0.104,respectively). CONCLUSION:The scotopic pupil sizes preoperatively are correlated with post-LASIK night glare during scotopic conditions,and the attempted correction of spherical equivalent is correlated with post-LASIK night glare in high myopia.