The present study investigated the effect of WhatsApp on language achievement and self-regulated learning of Iranian EFL learners through online Learning Management System (LMS) and WhatsApp as a supplementary treatment to the experimental group. To this purpose, an experimental design was used in a period of a three-month semester. The participants consisted of 24 Iranian male and female students studying in Iran Language Institute (ILI) in Sanandaj, Iran who were divided in two coeducational online classes in order to compare using LMS and WhatsApp in the experimental group (n=12) and only LMS for the control group (n=12). The data were collected through Oxford Placement Test (OPD) and Self-Regulated Scale (Seker), pre-test and post-test. In addition, the scores from the pre-tests and post-tests were analyzed via SPSS using the Kolmogorove-Smirnove test, descriptive statistics and ANCOVA analysis. The findings indicated that, WhatsApp as treatment and a supplementary medium to LMS had a significant effect on language achievement of Iranian EFL learners in the experimental group. The second finding showed that WhatsApp affected self-regulated learning of Iranian EFL learners for the same group. In both cases, the experimental group outperformed the control group due to the effectiveness of WhatsApp in the post-test. Finally, several merits and demerits of using WhatsApp along with LMS were discussed. The findings offer significant implications for online EFL classes.
