Compared to the other English medium instruction (EMI) issues, assessment has received very scant research attention. A complex issue in EMI assessment relates to the role of English in measuring learning outcomes, and whether or not language should be assessed along with technical content. Combining questionnaire and semi-structured interviewed data, this study explored the English-related assessment practices and beliefs of native-Arabic and non-native-Arabic faculty members teaching EMI scientific majors at eight Saudi universities. Two hundred and forty-nine faculty members completed the questionnaire, whereas 20 faculty members were interviewed. The results showed that the content teachers do not give much weight to language quality when evaluating students' written or oral performance. Compared to native-Arabic peers, the non-native-Arabic teachers, who intuitively have little or no translanguaging in their instruction, were found to pay slightly more attention to evaluating students' English and to considering it in assessing students' academic performance. Meanwhile, the interviews revealed that the teachers' negative language-related assessment attitude has been shaped by the view that they are non-responsible for correcting students' English, and by the too many language errors noted in students' performance. Finally, the teachers' highly-rated language assessment self-efficacy beliefs did not match their actual assessment practices.