Reading ability in English is decisive in determining the academic achievement of university students who study the English language, or any other subject in English. Extensive research has been conducted to explore whether ESL/EFL reading problems are language-specific or general reading problems. In this regard, previous research on the relationship between L1 and ESL/EFL reading abilities in different languages refers to various degrees of interdependence between L1 and reading in ESL/EFL. Yet, little attention has been paid to investigating the relationship between reading ability in English (L2) and Arabic (L1). This study examines whether university students' L2 (English) reading ability significantly correlates to that in L1 (Arabic). The study achieved this objective by administering two standardized reading tests in English and Arabic on 36 Arab university students who studied English language and literature. To assess the participants' overall EFL proficiency level and to test Cummin's Threshold Hypothesis, the researcher got the study participants to take a standardized EFL test. Data obtained was quantitatively analyzed. The results of the study showed that reading abilities in EFL and Arabic moderately correlated only at advanced-level EFL proficiency, which comes in agreement with Cummin's hypothesis. Results are discussed and pedagogical implications are also made