This study aimed to examine the relationships between motivational variables, self-regulated writing strategy use and writing competence with 511 fourth graders in Hong Kong. The high writing achievers reported a higher level of motivation, i.e. self-efficacy, task values (i.e. interest and utility) and growth mindset in English writing than the low writing achievers. The high achievers also used various self-regulated writing strategies more frequently than their low achieving counterparts. Self-efficacy and growth mindset were found to be almost equally important predictors of strategy use, while the impacts of interest and utility were weaker. The results indicated that self-regulated learning and competence in English writing can be improved through the promotion of motivation. This study highlights the influence of the social-cultural context on motivation. More importantly, growth mindset may emerge as a new research agenda in English as a Second/Foreign Language (ESL/EFL) writing.