This study examines how Nguyen Tat Thanh University in Vietnam's English language proficiency is affected by Content and Language Integrated Learning (CLIL). Using a mixed-methods approach, the study investigates how CLIL affects students' motivation to use English in academic contexts as well as their speaking, listening, reading, and writing abilities. While the quantitative phase used pre- and post-tests to measure changes in language proficiency, the qualitative phase involved semi-structured interviews with five faculty members and twenty students. The findings show that all four language skills have significantly improved, with speaking and writing exhibiting the biggest gains. Students also reported a deeper comprehension of subject-specific vocabulary and a greater desire to use English for academic purposes. These findings suggest that CLIL effectively enhances both language proficiency and student motivation by integrating content with language learning. The study also highlights the need for further research on targeted support strategies for students with lower proficiency levels. This research contributes to the growing body of literature on CLIL, offering insights into its application in Vietnamese higher education and its potential to improve English language outcomes for non-English major students.