The purpose of this study was to examine the causal relationships between S-OJT trainer preparation, self-efficacy as a trainer, trainers' delivery of S-OJT, and organizational commitment as a consequence of employing S-OJT. This study proposed a theoretical model from the review of related literature and then empirically investigated the fitness of the proposed model. This study was conducted in a life insurance company in Korea. A questionnaire was distributed to 334 randomly selected S-OJT trainers in Seoul. There were 235 usable questionnaires. structural equation modeling and principal factor analysis were applied to conduct a data analysis. The results showed that the chi-square was significant, along with good model fit indices. As a result, the causal links in the proposed model were established and these results fully supported the study hypotheses. Finally, the study discussed some implications for HRD, focusing on S-OJT.