Object: Fatigue is well established in causing significant decrements in performance and aviation safety. The modafinil is one of the fatigue modulating drugs in the military field. The objective of this study was to evaluate side effects of modafinil in grounding tests and to efficacy of modafinil for sustaining alertness in ROKAF pilots. Method: In grounding tests, the 44 pilots were participated and took one modafinil(200 mg) in 8 am and 4 pm each time, and monitored vital signs and side effects for 3 days. In simulator study, the 20 pilots were participated in double blinded randomized control study. We checked subjective self-reporting scale, korean profile of mood status, flying maneuvers, and stress hormones. We analysed paired t test and repeated measured ANOVA tests. Results: After medication of modafinil, participants were increased blood pressure, heart rate and temperature in the first day and recovered in the second day except systolic pressure. The percentage of side effects is 27.3% and disappeared in the second day. In simulator study, modafinil did not affect in subjective and objective scales. Conclusion: For using modafinil in military pilots, we need to evaluate grounding test for screening sensitive pilots, and modafinil was effective in the management of alert enhancing