This study investigated mediating effects of work engagement facets (vigor, dedication, and absorption) on the relationships between challenge-hindrance stressors and two kinds of organizational citizenship behaviors (OCBs). Participants were recruited from an online panel of a survey company in South Korea, and 353 employees completed a cross-sectional questionnaire. The results of path analyses and bootstrap analyses indicated that challenge stressors showed positive indirect effects on OCBs through increased vigor and dedication, whereas hindrance stressors exhibited negative indirect effects through decreased vigor and dedication. In addition, facets of work engagement displayed distinct patterns in terms of their mediating effects, in that dedication consistently showed larger effect sizes compared to vigor and absorption. Moreover, challenge stressors were observed to have both direct and indirect effects on OCBs, whereas hindrance stressors were found to have only indirect effects. Based on these research findings, theoretical and practical implications were discussed, along with limitations of the study and suggestions for future research.