This comparative and analytic study in two universities, Al-Jabal Al-Garbi University and Nasser International University in Libya, addressed and investigated the attitudes and preference of Libyan students and teaching staff toward the use of English, Standard Arabic or English Arabic Bilingualism as medium instruction in science and engineering education. It further investigated the relationship between attitudes toward language of instruction and students\teaching staff background variables such education, gender and language proficiency and lastly, the impact of language of instruction on quality of science and engineering education in Libya. The formerly published literature and studies were consulted to gather as much information about the topic as possible and to provide a solid base for the current study. Researcher adopted a mixed methodology, both quantitative and qualitative approach: Questionnaires and Interviews. Questionnaires were collected from both teaching staff and students of respective universities with prior consent and information about the study. Quantitative data is analyzed using SPSS software 17. Interviews were conducted from the teaching staff of both universities in order to gain in-depth insight on the topic of research and the collected data was analyzed by using Manual Coding Method. The result of collected data from Al-Jabal Al-Garbi University showed that students tend to favour Arabic-English Bilingualism, then Standard Arabic as a medium of instruction while students of Nasser International University tend to favour Arabic-English Bilingualism, then English. The teaching staffs of both the universities tend to strongly favour Arabic-English Bilingualism and English, and Standard Arabic was least preferred. The interview data showed that teaching staffs appreciate mostly English as a language of instruction, since it is the international language. English was recognised as important and necessary for a number of reasons, such as it has an impact on quality of education, its being the language in which most science and engineering text is written, most textbooks and journals are written, most data published online, and English opens many opportunities for future progress and development for both individual level and national level as well. On the basis of findings of the research conclusions are drawn and recommendations are made.