The present study highlights the significance of online self-regulated learning (SRL) in language education by investigating its impact on English as a foreign language (EFL) achievement. It focuses on the self-reported use of online SRL by focusing on six dimensions: goal-setting, structuring the environment, task strategies, time management, helpseeking, and self-evaluation, and potentially their power in predicting L2 achievement. Employing quantitative explanatory design, this study was conducted at an English preparatory class of a state university in Turkey with 91 undergraduate Turkish learners of EFL. Data were collected through a five-point Likert-type Turkish version of the Online "Self-Regulated Learning Scale" (Korkmaz & Kaya, 2012), initially developed by Barnard et al. (2009). As for the dependent variable of achievement, summative scores of two exams measuring both receptive and productive skills were gathered. The results suggest that the participants were medium to high level online self-regulated learners. Among the online self-regulation strategies, they report structuring their studying environment as the most frequent behavior, by seeking help from others and setting goals. The most significant positive correlation was observed between time management and goal-setting strategies, with a large effect size of d= 0.56. Our multiple regression model predicted 14% of the variance in language achievement scores; more specifically, employing help-seeking strategies was the strongest predictor of language achievement scores of Turkish EFL learners. The findings emphasize the importance of online self-regulation research and encourage online self-regulation implementation in the field.