This quantitative study investigated the relationship between learners' online self-regulation and their self-efficacy in the context of learning English as a foreign language (EFL). We collected data from two surveys, the online self-regulated English learning (OSEL) and the English language self-efficacy (ELSE), among 424 university students in China. Principal component analyses showed that the OSEL included six sub-scales, namely, goal setting, environment structuring, task strategies, time management, help seeking and self-evaluation, while the ELSE consisted of four factors targeting self-efficacy in listening, speaking, reading, and writing. The correlation analysis confirmed the associations between all scales of the OSEL and those of the ELSE. Furthermore, regression analysis revealed that self-evaluation was the most powerful predictor for explaining participants' variance of self-efficacy in English listening, speaking, and reading. Moreover, learners' environment structuring could significantly explain their self-efficacy in both speaking and writing, whereas goal setting could only predict students' self-efficacy in writing. These findings reveal the intricate relationship between online self-regulation and self-efficacy among the EFL learners, and further highlights the positive role of learners' self-evaluation, environment structuring and goal setting for explaining their English language self-efficacy. Pedagogical implications and future research are discussed at the end of this paper.