This study investigated the relationships between struggling writers' motivation (i.e., interest, self-efficacy, and growth mindset) and their use of self-regulated learning (SRL) strategies (i.e., planning, text-generating, self-monitoring, and collaborative learning) and writing competence in an English as a foreign language (EFL) context. Participants were 368 primary students in Hong Kong who scored 15 or less out of 48 marks in a writing test. They reported a generally moderate level of motivation and lower medium level of SRL strategy use. Especially, the participants reported a low level of interest. Results of structural equation modelling (SEM) suggested that growth mindset had the strongest positive correlations with the struggling EFL writers' use of SRL strategies. Both self-efficacy and interest also had positive correlations with the students' SRL strategy use, but only self-efficacy had significant and positive relations with their writing competence. Implications for English teachers to improve instruction for struggling EFL writers' in order to promote their motivation and SRL strategy use are provided and suggestions for future research are also discussed.