Based on self-regulation theories of stress processes, this study proposed a model to examine the within-person mediation relationship between morning commuting stressors and self-regulation at work via morning commuting strain. In addition, the study examined the moderating roles of daily task significance, daily family interference with work, and commuting means efficacy in this mediation model. Results from 45 bus commuters’ daily diary data over a period of 15 workdays indicated that the amount of morning commuting stressors experienced by the bus commuters was positively related to their morning commuting strain, which, in turn, had a negative impact on self-regulation at work. At the within-person level, daily task significance buffered the negative indirect relationship between morning commuting stressors and self-regulation at work via morning commuting strain, whereas daily family interference with work in the morning exacerbated this negative indirect relationship. Further, at the between-person level, commuting means efficacy buffered this negative indirect relationship such that the negative indirect effect was weaker for workers with higher (vs. lower) commuting means efficacy. Theoretical and practical implications of these findings are discussed.