While workplace learning includes formal and informal learning, the relationship between the two has been overlooked, because they have been viewed as separate entities. This study investigated the effects of formal learning, personal learning orientation, and supportive learning environment on informal learning among 203 middle managers in Korean commercial banks. To control the common method biases, the predictor and criterion variables were measured at different points in time with two separate sets of questionnaires. The results from using structural equation modeling showed that the proposed model indicated a better fit to the data than alternative models. It was found that formal learning and personal learning orientation have significant and positive impacts on informal learning. Although a supportive learning environment did not have a direct effect on informal learning, it had a modest but significant indirect effect on informal learning through formal learning. Implications for future research and practices are also discussed. (Contains 1 figure and 4 tables.)