This study investigated the effect of using authentic versus non-authentic materials on the motivation and also reading comprehension of Iranian high school EFL learners. For achieving this end, 100 Iranian high school EFL learners were selected randomly from among third-grade students of a high school in Marivan. Through administering a proficiency test (Oxford Placement Test, 2001), 60 of them were chosen who were at the same level of English proficiency. For the main phase of the study, these 60 students were assigned randomly into two groups of 30 as experimental and control groups. Of course, a motivation questionnaire (Salimi, 2000) was administered to the students of two groups two times, at the beginning and toward the end of the study to measure the difference in their motivation to learn English. The design of the study was true experimental. The independent t-test was run to compare the experimental and control groups'means on the pretest and posttest of reading comprehension and the first and second motivation tests. The results indicated a significant positive effect of using authentic materials on the motivation and also reading comprehension of the participants. The experimental group outperformed the control group on the posttests of motivation and reading comprehension
