This research investigates whether there is any significant difference between the predictive power of vocabulary breadth and the reading subtests of IELTS and TOEFL. Iranian EFL participants (223) answered Vocabulary Levels Test (VLT), sample IELTS and TOEFL reading subtests. Linear regression analysis results show that VLT provides a significant amount of prediction on IELTS and TOEFL reading subtest, R2 = 0.274, 0.298, respectively. The results for the participants with different levels of vocabulary knowledge, based on VLT percentile scores, show that, for low group, VLT provides 0.123% prediction for IELTS reading subtest and nothing for TOEFL reading subtest. For middle group, VLT provides no prediction on IELTS and TOEFL reading subtest. For high group, the amount of prediction provided on IELTS reading subtest is 0.130 and that on TOEFL is 0.209. Also, analysis was conducted to determine the most related variable to VLT. The results show that TOEFL reading subtest is more associated with vocabulary breadth than IELTS. The study discusses a few implications.