this study was an attempt to investigate the effect of using c-test passages on the reading comprehension and incidental vocabulary learning of iranian intermediate efl learners. the participants were 60 male efl learners at kish mehr institute in garmsar. in fact, there were two groups, an experimental group and a comparison group with 30 students in each. the participants were pretested through the reading comprehension section of toefl and a teacher-made vocabulary test. the results of the pretesting stage indicated that there was no significant difference in reading and vocabulary knowledge between the two groups at the outset of the study. this was followed by the instructional period. in each session during the instructional phase, which lasted for 10 sessions, the students in the experimental group received a c-test passage of the standard format and those in the comparison group received the same passage in full followed by some multiple-choice comprehension questions. after the instructional period was over, the students in both groups were pretested through the same reading comprehension and teacher-made vocabulary test. the data analysis in this study was carried out through an independent samples t-test. performing t-test showed that the p-value was lower than the level of significance and it was enough for the researcher safely reject the null hypotheses.