Back ground: The biomechanical impact of flap creation may be important in explaining changes in the curvature of the residual stroma after flap creation which plays a critical role in the development of ectasia. OBJECTIVE: To evaluate the impact of the creation of corneal flaps with mechanical microkeratome versus femtosecond laser on the biomechanical properties of the corneas. METHOD: This study included 100 eyes of 50 patients (Microkeratome Group) Compared with 100 eyes of 52 patients (Femtosecond Group) with myopia with or without astigmatism. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with Ocular Response Analyzer before and1, 3,6and 12 months after surgery. We also investigated the relationship between these biomechanical changes and the amount of myopic correction. RESULTS: Corneal resistance factor and hysteresis was changed significantly after flap creation in both groups. In Moria2 group, they decreased significantly from 11.55 ± 1.29 mm Hg and 11.68±1.40 mm Hg to 9.47 ± 1.29 mm Hg and 8.49 ± 1.54 mm Hg, respectively) (P <.0001). In femtosecond group, they decreased from11.51 ± 1.25 mm Hg and 11.66±1.41 mm Hg to 9.49 ± 1.30 mm Hg and 8.5 ± 1.53 mm Hg, respectively (P <.0001). The ablation depth (P=0.650), residual corneal thickness (P=0.442), and postoperative corneal curvature (P=0.354) were not significantly different between femtosecond group and Moria2 group after surgery. CONCLUSION: Both femtosecond LASIK and Moria2 LASIK can affect the biomechanical strength of the cornea depending on the amount of myopic correction. The amount of biomechanical changes is larger after LASIK with mechanical microkeratome than after femtosecond from a biomechanical viewpoint.