English is an access to a global society (Normark, 2013), which implies studying a specific subject area through English is crucial in today's educational arena. The reason behind this is that English is a motive for universities to gain a global status as Coleman (2006) argued. Thus, the focal point of this study is to reveal motivational variations of students and lecturers toward English-Medium Instruction (EMI) because motivation may be an influential factor determining the success of EMI implementations. To this end, the study was designed as a mixed methods research to reach a deeper understanding of the issue. The participants were mechanical engineering students and lecturers at a state university in Turkey. In this regard, a Likert-type questionnaire was adapted to examine what factors had an impact on motivation of participants toward EMI. For the analyses of quantitative data, descriptive statistics were used to obtain mean and standard deviation scores; and MANOVA test was utilized via inferential statistics to see whether the year of study was a determinant for the motivation of students. Moreover, focus group interviews were conducted with students whilst lecturers were interviewed individually. Qualitative data obtained from interviews were analyzed using inductive content analysis. The results indicated no significant differences among the first, second, third and fourth year students' motivation toward EMI; yet, it was found that the first year students were slightly more motivated toward EMI. Further, instrumental motivation appeared to be more dominant and lecturers' motivation toward EMI varied depending on numerous reasons.