The present study primarily aims to investigate the relationship between Pakistani students' receptive vocabulary growth and their reading development at two different points: at the beginning and the end of English course. The standardized vocabulary size test (VST) and reading comprehension test (TOEFL) were administered to 123 first year postgraduate university students. To analyse the data, both descriptive and inferential tests were performed in SPSS (version, 21). The findings of the descriptive statistics showed a change in the mean scores of participants' vocabulary on 14,000 words list at the beginning of the English course (M=35.00) and (M=40.80) at the end of the English course respectively. The findings of the paired t-test revealed that the change was significant at p<0.001. The findings of correlation test indicated that students' vocabulary size and their reading ability were closely associated at (r = 0.76). The findings of the simple linear regression also generated acceptable model where 58.2% of the variance in the dependent variable (reading comprehension) was predicted by the independent variable (vocabulary size). This study has some implications for teaching and learning of the English language.