The present research was conducted to examine the relative effectiveness of two instructional approaches to second language vocabulary learning: the "Reading Only" (RO) approach and the "Reading Plus" (RP) approach. To carry out this study, sixty EFL students from Shahed Pre-University Center of Isfahan were selected and divided into two groups of thirty after a standardized test (The Nelson Test) was administered to120 of them to determine group homogeneity. In the "Reading Only" group, the students only read several reading passages. In the "Reading Plus" group, the subjects read passages and then did a series of text-based vocabulary exercises. The analysis of the results revealed a significant difference between the two groups. The results indicated that "Reading Plus" group had significantly outperformed the "Reading only" group. This strongly suggests that the "Reading Plus" approach to foreign language vocabulary learning is highly effective in promoting a deep and stable knowledge of vocabulary.