The present study was an attempt to explore the comparative effects of using Massive Open Online Courses (MOOC) and Mobile Instant Messaging (MIM) on reading comprehension skills of Iranian English as a foreign/second language (EFL) learners. To achieve this objective, 100 Iranian learners studying English at Tehran Language Institute in Khorramabad were selected based on convenience sampling. They took the Oxford Placement Test and based on the results, 40 intermediate-level learners were selected and assigned to two groups in intact classes. Then, both groups were given the reading section of the Preliminary English Test (PET) before the treatment to determine the participants' reading comprehension level at the beginning of the research.  During the treatment, both groups were taught the same teaching materials, but the materials were presented through two different online tools: Skyroom application as the MOOC platform and WhatsApp as the MIM. After the treatment, a reading posttest was administered to both groups. The data were analyzed through a series of independent and paired samples t-tests. The results indicated a significant difference between the post-test reading comprehension performance of the two groups. It was revealed that using the MOOC platform had a statistically significant effect on learners’ reading comprehension performance, while the effect of using MIM was not significant. The findings imply that online language teaching platforms might have differential effects on language learning and that language teachers need to consider the differences among the tools in making decisions as to when and where to use which online tools.