One of the driving forces for a wider adoption of English as a Medium of Instruction (EMI) in higher education is that students may demonstrate improvements in English language proficiency through an increased English exposure from content learning. However, to what extent previous English exposure has an impact on students' learning experiences remains unanswered. This paper contributes to filling this gap by analysing quantitative data of 73 undergraduate science students from Hong Kong, classified by their prior English language exposure. Students completed a survey exploring their perceptions of their (1) exposure to EMI prior to university admission and the actual language use in classrooms; (2) English abilities in different learning activities; (3) English language challenges; and (4) learning strategies. Results showed that students' perceptions of EMI learning varied with their levels of English exposure prior to university admission. Despite encountering more difficulties in using English among first-year students with lower-level English exposure, all students perceived the importance of English skills in science education and adopted different learning strategies to overcome the EMI study challenges.