Objectives The suicide rate in Korea is one of the highest among all members of the Organization for Economic Cooperation and Development. Gatekeeper training is one of the major projects for the national suicide prevention strategy in Korea. The Gatekeeper Behavior Scale (GBS) is a self-reported questionnaire used to evaluate the effects of gatekeeper training. This study aimed to validate the Korean version of the Gatekeeper Behavior Scale (K-GBS). Methods The GBS was translated into Korean, then back-translated to the original language to verify the translation accuracy. Nine hundred middle and high school teachers who participated in gatekeeper training for suicide prevention were included in this study. The construct validity was tested using confirmatory factor analysis. The internal consistency was assessed using Cronbach’s alpha. Results Confirmatory factor analysis showed that the K-GBS comprised of three factors (preparedness, likelihood, and self-efficacy) with an acceptable model fit (Tucker-Lewis index=0.99, comparative fit index=0.99, root mean square error of approximation=0.03). The Cronbach’s α coefficients were 0.95 for the total scale, 0.94 for preparedness, 0.89 for likelihood, and 0.93 for self-efficacy. Conclusion The K-GBS showed good construct validity and internal consistency. Therefore, it can be a useful tool for assessing the effects of gatekeeper training on suicide prevention in Korea.