Responding to the controversies in the results of past studies regarding the impact of language proficiency on learners' use of language learning strategies, this article reports the effect of language proficiency on the strategy use of Iranian English learners across two different settings, namely ESL Malaysia, and EFL Iran. Some 157 Iranian college level male English learners were randomly selected from both settings as establishing the ESL and EFL groups of the study. They were further grouped into their appropriate levels of language proficiency based on their language institutes' placement tests, and their selfassessed proficiency report. Version seven of Oxford's SILL was adopted to collect information on the learners' perceived use of language learning strategies regarding the overall SILL and the six strategy categories included in SILL. Statistical techniques, namely ANOVA and MANOVA, were separately utilized for analyzing the data collected for ESL and EFL groups. To gain rich data, the researchers conducted a semi-structured one-on-one interview with 12 students (six from each setting) to elicit information on the participants' incentives for learning and using the target language in their related settings (Iran and Malaysia). The results of the study show that language proficiency significantly affected the ESL learners in using both the overall SILL and the six strategy categories included in SILL. In contrast, EFL learners across low, intermediate and advanced groups of proficiency did not significantly differ from each other with respect to overall use of the SILL and its six strategy categories.