The purpose of this study was to investigate the effects of scaffolded English writing instruction using mind mapping tools on English narrative writing proficiency among Chinese middle-school EFL students. Specifically, we examined its effects on four subcomponents of narrative writing compositions: lexical complexity, grammatical complexity, accuracy, and fluency. Non-equivalent group pre-test–post-test design was employed in this study. The participants were 55 eighth-grade students in an English class. The data were collected through two writing tests administered before and after a two-month intervention. The results showed that students’ writing demonstrated significant improvements in lexical complexity, grammatical complexity, accuracy, and fluency. These findings suggest that scaffolded writing instruction with mind mapping can effectively enhance multiple dimensions of writing skills in adolescent EFL learners. This study provides insights into the application of using mind mapping to scaffold EFL learners’ narrative writing proficiency.