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This study explored the effect of using Self-Regulated Strategy Development (SRSD) instruction on the persuasive writing and self-efficacy of Iranian EFL learners and compared the effectiveness of such instruction with nonstrategy-based (i.e., traditional) instruction. In so doing, this study followed the SRSD model, using a mnemonic and transition word chart, essay examples, and a graphic organizer. To achieve the objectives, 60 Iranian EFL undergraduate students at two universities participated in this study, which used a pretest-posttest control group quasi-experimental design. The analyses of covariance on the persuasive essays and self-efficacy tests in the control and experimental groups revealed that both SRSD and non-SRSD instructions had a positive impact on the participants' persuasive writing ability. But the effect of SRSD instruction was significantly greater on the participants' writing (i.e., format and content, organization and coherence, sentence construction and vocabulary in writing). In addition, the self-efficacy of the SRSD group improved, but the difference in posttest self-efficacy scores between the SRSD and non-SRSD groups was not statistically significant. The findings draw language instructors' attention to the metacognitive dimension of writing and importance of teaching self-regulatory strategies as a way for achieving autonomy and self-efficacy in writing.