The study examines direct and indirect impacts of organizational commitment on employee motivation through two mediating factors – opportunistic behavior and knowledge sharing – in Vietnamese enterprises. The samples were selected by the non-probability sampling method followed convenient sampling, relatively stratified by localities in Vietnam. The sample size was 636 employees in Vietnamese enterprises. The number of collected online questionnaires was 379, while the number of valid questionnaires was 329. In the direct survey, the number of distributed questionnaires was 750, while the number of collected questionnaires was 421 and the number of valid questionnaires was 307. The total number of valid questionnaires used for analysis was 636. The study used quantitative methods with structural equation modeling analysis. The results indicate that among the components of organizational commitment, normative commitment has both direct and indirect impacts on employee motivation through two mediating factors: opportunistic behavior and knowledge sharing. Meanwhile, affective commitment has only an indirect impact on employee motivation through these mediating factors. Continuance commitment has both direct and indirect impacts; however, it has only an indirect impact on employee motivation through opportunistic behavior. In addition, the results show opportunistic behavior has a negative impact on the knowledge sharing of employees in enterprises.