Abstract-The present study aims at studying the effect of immediate and delayed feedback on the depth of vocabulary knowledge. To this end, two classes were selected from Sokhansara institute of those who were studying at the intermediate level. But, to ensure homogeneity, an OPT was given based on which two groups were selected, one acting as the immediate feedback group (IFG) and the other as the delayed feedback group (DFG). In the next stage, a pretest which was adapted from Read's Word Association Test was given to assess the students' depth of vocabulary knowledge before treatment. After that, students in IFG received feedback over their lexical errors immediately in the presentation stages of the lessons, while in DFG, feedback was provided in the practice and production stages of the lessons. At the end of the semester, a parallel post test was given to assess the students' depth of vocabulary knowledge. As to the analysis of the results, a paired sample Students' T-Test was run on SPSS to compare the scores of participants in pretest and posttest within each group. An independent sample Students' T-Test was also run between the post test results to check the differences between two experimental groups. The findings of this research indicate that using delayed feedback has a positive impact on enhancing the depth of vocabulary knowledge of EFL students at intermediate level.Index Terms-corrective feedback, dimensional approach to depth, immediate and delayed feedback, vocabulary knowledge dimensions, word association test