Background: While self-regulated learning (SRL) strategy-based writing instruction has been proposed in English as a foreign language (EFL) classrooms, there is insufficient evidence with Japanese EFL learners and little discussion on incorporating online resources into SRL strategy-based writing instruction, despite the availability of various online platforms. Objectives: This study proposed an SRL strategy-based instruction for technology-assisted writing and explored its immediate and sustained impacts on Japanese tertiary EFL learners' writing performance, reported use of SRL strategies, self-efficacy beliefs and perceived acceptance of technology. Methods: The research design used was a pre-experimental pre-test, post-test and delayed post-test design with a quantitative approach using convenience sampling. Participants were 44 students enrolled in an academic writing course at a Japanese university. Over an 8-week period, these students received SRL strategy-based writing instruction supported by online writing resources. The research instruments included writing tests and questionnaires assessing SRL strategies, self-efficacy and technology acceptance at the beginning of the intervention (Time 1), immediately after the intervention (Time 2) and 1 month after the intervention (Time 3). The data analysis techniques involved ANOVA, post-hoc tests, and examination of the effect sizes. Results and Conclusion: The results showed statistically significant improvements in students' writing performance, SRL strategy use, self-efficacy and technology acceptance from Time 1 to Time 2 and persistent impacts at Time 3, suggesting the intervention's potential to improve EFL writing. This study contributes to EFL writing pedagogy by exploring the immediate and sustained impacts of teaching SRL strategies in a technology-enhanced writing environment.