To determine the effect of suction duration on thickness and diameter of corneal flap created by microkeratome in porcine eyes in laser in situ keratomileusis (LASIK). 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. The flap thickness of group 1, group 2 and group 3 was (146.05±13.46)µm, (157.35±18.95)µm and (169.25±21.02)µm, 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±0.19)mm, (8.89±0.24)mm and (9.06±0.18)mm, respectively. A statisti-cally significant difference was found among groups (P<0.01). In LASIK in porcine eyes, an increase in suction duration resulted in a thicker and greater flap.