ABSTRACT Acculturation strategies contribute to international students’ self-assessment of Mandarin learning (ML) performance, but the mechanism remains unclear. This study employed a convergent design of mixed methods and explored the roles of acculturation strategies and local support resources in international students’ (ISs) self-assessed ML performance in Chinese universities. The quantitative findings based on the questionnaire survey (N = 520) found that ISs’ Mandarin level was positively associated with the integration strategy and local support resources (i.e. Chinese teachers and Chinese friends). Besides, integration and marginalisation mediated the relationship between support resources and self-assessed ML performance, with integration acting as a more positive mediator compared with marginalisation. Further qualitative findings based on the longitudinal data (i.e. reflective journals) supported the positive roles of integration and local support resources in self-assessed ML performance. Moreover, this study identified how ISs improved their Mandarin through positive adjustments in their acculturation strategies (e.g. from separation to integration) and active mobilisation of local support resources. These findings provide a richer understanding of the complexity and dynamism of ISs’ self-assessed ML performance. Implications were provided for ISs and Chinese universities concerning ML and support services.