The present study aimed to investigate the effect of the language of instruction on the participants’ acquisition of the scientific terms with respect to their knowledge, usage, proficiency, adoption and evaluation in two Arab universities. The faculty members and the students of the faculties of Engineering and Medical sciences in the Jordan University of Science and Technology (JUST), where the medium of instruction is English , and the University of Damascus (UD), where Arabic is the medium of instruction, were the participants in the study. They were 991 students of different scientific fields at JUST, and 729 students at the UD. The students ranged from third-year level to graduate studies level. Also, 132 faculty members in different scientific fields at JUST, and 109 faculty members at the UD participated in the study. The results of the study show that there were statistically significant differences between the means of the criteria of knowledge, usage, proficiency, adoption and evaluation of the Arabicized terms due to the effect of the language of instruction (i.e., English language) in favor of JUST, and there were statistically significant differences between the means of the criteria of knowledge, usage, proficiency, adoption and evaluation of the Arabic equivalent terms due to the effect of the language of instruction (i.e., Arabic) in favor of the UD. The results of the study, also show that the percentage of the participants’ responses to the items that ask about their use of the Arabicized scientific terms in JUST is 93.3%, which is higher than that in UD which was 27.8%. Also, the percentage of the participants’ responses to the items that ask about their use of the Arabic equivalents in UD is 72.2%, which is higher than that in JUST which was 6.7%. The result is ultimately due to the effect of the medium of instruction at each university. In light of the findings of the study, it was recommended that research in different scientific fields other than medical and engineering fields be conducted to explore the role of the medium of instruction in the acquisition of the scientific terms
