Although there is a wide range of studies on the use of PowerPoint Presentations (PPP) in different fields, few studies have investigated the effects of different aspects of multi-modal PowerPoint presentation on the language comprehension of foreign language students. This study was conducted to investigate the effect of PowerPoint-supported (PPS) lectures on immediate comprehension and longer term retention of the content by foreign language University students. For this purpose, 69 students of teaching English as a foreign language (EFL) enrolled in language teaching methodology course were randomly assigned into three groups: A. PPS lectures with slides' contents being read out, B. PPS lectures with slides at propositional level, and C. oral presentation with no multimedia. Pre-test Post -test control group design was applied in the study. The treatment procedure took twelve sessions each lasting for an hour. During each session, the students were presented with a lesson on language teaching methodology followed by a posttest of immediate recall. Finally, one month after the last lecture all the groups sat for the delayed posttest. It was found that learners' comprehension improves significantly both immediately and in the long run when they are provided with PPS lectures with slides at propositional level. To be efficient, the content of the slides in PPS lectures must be selected and designed with great care so that key terms, issues and main ideas are covered. Copying course material into slides and including too much explanations and details will have an adverse effect on students' retention and recall.