This article explores the relationship between Turkish undergraduate students’ language learning mindsets, English language achievement, and English medium instruction (EMI) academic success. Student test score data on an EMI course and an English language course were collected from fourth year students studying mechatronics engineering (n = 68) and business administration (n = 75) at a public university. Students also responded to the Language Learning Mindsets Inventory (Lou & Noels, 2019). Regression analyses revealed that both incremental (positively) and entity (negatively) mindsets predicted academic success in engineering. Neither mindset was a statistically significant predictor of mechatronics engineering students’ English language achievement. Business administration students’ academic success and English language achievement were both statistically significantly predicted by both incremental (positively) and entity (negatively) mindsets. These results are discussed according to discipline-based differences in EMI courses and pedagogical implications are explored.