With the large increase in online English language learners, there is a need to explore how those learners practise self-regulated writing in such an autonomous learning context. This article reports on an exploratory study of self-regulated learning strategies used by two writing-proficiency groups (low and high) of Saudi English majors within an online context. Data were collected from a total of 50 (high proficiency = 23 and low proficiency = 27) students using video-stimulated recall of two online writing tasks. Quantitative analysis of the students' stimulated recall data revealed that students in both proficiency groups used 11 self-regulated strategies to complete the two online writing tasks. Results also revealed a positive correlation between self-regulated learning strategy use and the students' writing proficiency level. The chi-square test analysis revealed statistically significant differences between the two groups in six strategies overall favouring the high writing-proficiency group. Further qualitative analysis of the stimulated recall data within the framework of sociocognitive theory revealed that the high proficiency students stood out from their low-proficiency counterparts in how they self-regulated their personal, behavioural, and environmental processes. Implications for writing instruction to improve students' writing performance in online learning contexts and future self-regulated writing strategy research are discussed.