This study, on the one hand, investigated whether or not strategies like Lexical Inferencing (LI) and Morphological Instruction (MI) can significantly affect English as a Foreign Language (EFL)learners’ reading comprehension, and on the other hand, it examined their effects on the learners’ vocabulary retention over time. For this purpose, 60 homogeneous EFLlearners were randomly assigned to two experimental and one control group each one consisting of 20 participants. After the pre-test, participants of the first experimental group received lexical inferencing strategy training for six 45-minute sessions. The second experimental group was also provided with morphological instruction for six 45-minute sessions and as for the control group, the participants followed their regular reading comprehension course without any specific strategy training. After the treatment, two post- tests with a short time interval were administered to the three groups and the obtained data were fed to different statistical tests to spot the probable differences among the three groups' first post- test performance as a measure of their learning differences and the second post-test performance as a measure of the learners’ vocabulary retention differences over time. Results of the paired t-tests for comparison of the within group differences showed that lexical inferencing instruction had statistically significant effect on EFL learners' reading comprehension development. On the other hand, it was found that morphological instruction had no statistically significant effect on EFL learners' reading comprehension development. The ANOVA analyses revealed that there was no statistically significant difference between the effects of lexical inferencing and morphological instruction on EFL learners' reading comprehension development. Furthermore, no significant difference was found between the effects of lexical inferencing and morphological instruction on EFL learners' reading comprehension development over time.
