In this paper, a study on the effectiveness of micro-peening was accomplished for improvement of fatigue characteristics for reduction gear of manned and unmanned aircraft. The Almen saturation curve was obtained by various peening injection pressure supplied from a commercial air jet peening machine. The effective micro-peening process condition was adopted as five bar. The four points rotary bending fatigue test was conducted by using test specimen made of AISI alloy that was carburized based on AMS standard in this work. From the fatigue test result, the fracture life of specimen peened by nozzle pressure with five bar and six bar was higher than the un-peened specimen by approximately 323 percent and 146 percent respectively. However, the fracture life of specimen peened by the nozzle pressure with six bar was lower by approximately 221 percent than the peened specimen by five bar. For this reason, the peening nozzle pressure with five bar was decided as the optimum micro-peening condition. Effectiveness of micro-peening was validated and this micropeening technique will be used for real manned and unmanned aircraft gear parts or other durability mechanical parts.