This study aimed to investigate the effects of using spacing and massed instructions on Iranian EFL learners’ learning of English prepositions. To this end, 48 Iranian male participants were selected among 78 students based on the results of the Oxford Quick Placement Test (OQPT). The participants were randomly divided into two experimental groups of spacing and massed instructions. Then, both groups were pretested through a researcher-made prepositions test. After pre-testing, the prepositions of “in, on, at, from, about, and across” were taught to the experimental groups through spacing instruction and massed instruction. In the massed class, the mentioned prepositions were taught during five sixty-minute sessions while in the spacing class with the same number of sessions, each sixty-minute session was divided into three 20 minutes. Also, the massed class was held once a week while the spacing class was held three times a week. After the treatment, the results of the descriptive statistics as well as paired samples t-test and independent samples t-test indicated that the spacing group had better performance than the massed group on the post-test. Also, there was a significant difference between the post-tests of both groups in favor of the spacing group.