Critical thinking, intelligence, and language aptitude are three cognitive factors, each, in its own way, influencing our lives. They are important in successful reasoning, problem-solving, and foreign language learning, and thus are worth studying regarding their influence on individuals' language-related skills, in particular, foreign language-related skills. This study used a correlational design to investigate how well the set of variables of critical thinking, intelligence, and language aptitude can predict Iranian EFL learners' reading comprehension ability, and to see which variable in this set was the best predictor. Additionally, the study explored whether the set could predict these learners' reading comprehension ability differently depending on their language proficiency. Fifty-seven university students majoring in English took part in this study. They were sixth- and seventh-semester undergraduate students at the University of Sistan and Baluchestan, and Farhangian University of Zahedan, Iran. The data were collected through an Oxford Placement Test, a Watson-Glaser Appraisal, the Wechsler Adult Intelligence Scale-Revised, The Colleges of Oxford University Classics Language Aptitude Test, and the reading comprehension section of a Michigan language proficiency test. Statistical analysis revealed that critical thinking, intelligence, and language aptitude allowed us to predict the participants' reading comprehension ability by as much as 83%. Language aptitude, with a unique contribution of 63% was the best predictor of the three. The results also showed that the predictive difference between the participants with high language proficiency and that of participants with low language proficiency was not statistically significant.