This study investigated the key determinants of Chinese students’ academic success indicated by their first semester GPA and credit hours earned in Korean universities. The determinants include demographics, prior achievement, academic self-efficacy, and Korean and English language proficiency. Questionnaires were issued and collected from 138 undergraduate and 63 graduate Chinese students studying in 27 different Korean universities. The findings of this study suggest that the Test of Proficiency in Korean (TOPIK) has a significant small to medium predictive effect on academic success and serves well as an admission requirement, especially for graduate students. The findings also highlight that both Korean and English proficiency influence on academic success in this particular context. The relationship of language proficiency and academic success is complicated, and this study contributes to the field by exploring this relationship in a less researched test, TOPIK and by investigating two languages at the same time. This study also contributes to the overall understanding of international university students’ academic success, in particular the success of Chinese students.