Objective: To investigate the effects of corneal epithelium on corneal curvature in patients with keratoconus. Design: This is a prospective, nonrandomized study. Participants: Fifty-nine eyes of 47 patients diagnosed as keratoconus and for whom corneal collagen crosslinking (CXL) was recruited in this study. Methods: This study is a single-center clinical trial. Pregnancy, lactation, connective tissue disease, corneal thickness below 350m, severe dry eyes, or scar of corneal surgery were exclusion criteria. Before and during CXL procedure after removing the corneal epithelium, maximum values of corneal apical curvature, simulated keratometry 1 (Sim-K1), simulated keratometry 2 (Sim-K2), temporal and inferior curvature values, all of which are 1.5mm from the corneal center, were calculated. These values before and after removal of epithelium were compared statistically. Results: Mean age of patients was 23.30 +/- 5.5 (12-38) years. Twenty-eight (59%) were male while 19 (41%) were female. Mean values measured before and after removing the corneal epithelium were: apical curvature; 59.19 +/- 7.2 (47.06-82.40) diopter (D) and 61.70 +/- 8.8 (49.19-92.66) D (p=0.001), SimK1; 47.57 +/- 4.3 (39.14-64.57) D and 48.23 +/- 4.3 (41.89-66.70) D (p=0.001), SimK2; 52.04 +/- 5.3 (43.56-69.34) D and 53.34 +/- 5.6 (43.73-70.89) D (p=0.001), inferior curvature; 53,85 +/- 5.2 (43.47-76.56) D and 55.05 +/- 5.8 (44.56-81.93) D (p=0.002), temporal curvature 49.49 +/- 5.1 (41.50-71.03) D and 51.53 +/- 5.4 (41.58-73.34) D (p=0.001), respectively. Conclusions: In keratoconus patients during CXL treatment, after removing the corneal epithelium, more steepness is detected in the curvature of the steeper area of the cornea. When evaluating patients with keratoconus, the masking effect of corneal epithelium on values of curvature should be taken into consideration.