This study investigated the effects of different text difficulty levels on Iranian EFL learners' foreign language reading motivation and reading comprehension. To fulfil this objective, 40 Iranian participants were selected among 50 students based on the results of Interchange Placement Test (Richards et al, Placement and Evaluation Package Interchange Third Edition/Passages Second Edition with Audio CDs, 2008). The pre-intermediate selected participants were then randomly divided into two equal groups; "i + 1" group (n = 20) and "i-1" group (n = 20). Afterwards, the researchers measured the participants' English reading comprehension by administering a researchers-made reading comprehension pre-test. Moreover, "Motivation for Reading Questionnaire" was also conducted. After the participants were all pre-tested, the treatment was practiced on the both groups. The participants in "i + 1" group received reading passages beyond the current level, on the other hand, the "i-1" group received those reading passages which were below their current level. After the instruction which lasted about 3 months, a modified version of reading comprehension pre-test was administered to the both groups as posttest and finally the data were analyzed by using paired and independent samples t-tests. Moreover, Students' answers to the questionnaire was also analyzed. The obtained results indicated that there was a significant difference between the post-tests of "i + 1" and "i-1" groups. The findings indicated that the "i + 1" group significantly outperformed the "i-1" group (p < 0.05) on the post-test. Furthermore, the results revealed that the 'i + 1' materials could help Iranian EFL learners increase their reading English motivation. This study has implications for teaching and learning reading comprehension.