It is of importance to foster ESL/EFL students to become more autonomous in their language learning. Project-based learning (PBL) is considered as one of the effective choices for teachers in order to trigger self-regulation among students. However, PBL seems to be still alien to many EFL teachers and students at the high school levels. Within such a context, this study, part of a project, aims at exploring EFL high school students' use of self-regulated language learning (SRLL) strategies for PBL. This study involved 147 EFL high school students from a high school in Vietnam in answering the questionnaire, and forty students of which took part in semi-structured interviews. The quantitative data from questionnaire were analyzed in terms of mean and ANOVA, while qualitative data from interviews were analyzed by the content analysis approach. The findings showed that research participants usually employed SRLL strategies for PBL. Moreover, the group of flexible use of strategies was applied more frequently than other six groups of strategies. Additionally, the frequency of EFL high school students utilized SRLL strategies for PBL similarly was not influenced by their levels of academic study. These preliminary findings are hoped to contribute to a better understanding of the use of SRLL strategies in implementing PBL.