This study investigated the influences of the use of self-regulated learning (SRL) strategies on students' self-efficacy in English writing. A total of 155 fourth graders from 1 government-funded primary school in Hong Kong completed a questionnaire on SRL strategy use and a questionnaire on self-efficacy in English writing. The students used planning strategies more frequently than the other strategy types (e.g., text generating). They had a higher level of self-efficacy in content than in the other aspects (e.g., language and grammar). The students with more SRL strategy use reported a higher level of self-efficacy. The use of SRL strategies had significant and positive relationships with the students' self-efficacy. In particular, the use of planning and self-monitoring strategies had the strongest correlations with self-efficacy. This study opens a new window to understanding how students' self-efficacy in English writing develops as a result of their SRL strategy use. We discuss practical implications for English as a second language/English as a foreign language classroom instruction. [Copyright of Reading & Writing Quarterly is the property of Taylor & Francis Inc.]