The current study aimed to explore the effects of integrating a selfregulated learning approach on self-efficacy in vocabulary learning. A group of 115 English as a Foreign Language (EFL) learners from a university in Japan participated in this longitudinal study. The participants were assigned as the treatment group, the contrast group 1, and the contrast group 2. Only the treatment group received the intervention based on the self-regulated learning approach. The participants completed a

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... ionnaire on self-efficacy in vocabulary learning three times and a vocabulary test twice. Multilevel analysis of change was employed to examine the trajectories of change in the participants' self-efficacy over the measurement occasions. The gain scores in the vocabulary test were submitted to analysis of variance. The results showed that the treatment group showed a steady increase in self-efficacy and vocabulary knowledge compared with the other two contrast groups. The findings from the current study provide empirical evidence suggesting that through a selfregulated learning approach, it might be possible to enhance self-efficacy, which in turn may contribute to the development of vocabulary knowledge.