AIM: To determine the effect of suction duration on thickness and diameter of corneal flap created by microkeratome in porcine eyes in laser in situ kerato-mileusis (LASIK). METHODS:Sixty porcine eyes were randomly assigned to three groups according to different suction durations:group 1 (10 seconds),group 2 (20 seconds),and group 3 (30 seconds).A Moria M2 microkeratome (Moria, France) with a 160μm head was used to create a corneal flap. Corneal flap thickness was measured by automated ultrasonic pachymetry, and the flap diameter was measured by a vernier caliper. RESULTS: The flap thickness of group 1, group 2 and group 3 was 146.05±13.46μm, 157.35±18.95μm and 169.25±21.02μm, respectively. There was a statistically significant difference among three groups (P=0.001). The mean flap diameter in groups 1, 2 and 3 was 8.63±0.19mm, 8.89±0.24mm and 9.06±0.18mm, respectively. A statisti-cally significant difference was found among groups (P<0.01). CONCLUSION: In LASIK in porcine eyes, an increase in suction duration resulted in a thicker and greater flap.