[Purpose] This study examined the effects of foot orthosis on the gait ability of college students in their 20s with flat feet. [Subjects and Methods] The subjects were 20 college students who had been diagnosed with flat feet. The subjects’ step time, step length, stride time, stride length, and gait velocity were measured using the VICON Motion System (Vicon, Oxford, UK) prior to and while wearing foot orthoses. The resulting data were analyzed using SPSS v. 12.0. [Results] The subject’s step time and stride time significantly decreased for both feet after they began using foot orthosis, and stride length and gait velocity significantly increased in both feet orthosis; however, step length did not significantly increase on either side. [Conclusions] College students with flat feet saw an improvement in elements of their gait while using the foot orthosis. The results of this study verified that students with flat feet might walk more efficiently if they received active gait training via long-term use of foot orthosis.