The study success of international students in Higher Education (HE) in English speaking countries has been a major concern for both the students and the host universities. However, studies on the predictive validity of established language tests, such as IELTS, are inconclusive (for an overview see Daller and Phelan 2013, Predicting international student study success. Applied Linguistics Review 4(1). 173–193). The present study explores the predictive validity of new test formats that could be used in the admissions process alongside the established tests to identify students who are at risk. In the long-term these new test formats have the potential to form the basis of a stand-alone admissions test. The formats under investigation are a gap-filling test (C-test) as test of general language proficiency and several measures of lexical richness (Guiraud, Guiraud Advanced, “D”; see also methodology). All measures were taken at the beginning of an academic year to predict the average grades at the end of the academic year (General Points Average/ GPA). In total 107 international students, mainly from China, with a wide range of subjects participated in the study. A multiple regression analysis including hierarchical models shows that the C-test and “Guiraud” have the highest predictive validity. Given the fact that these two measures can be administered quite easily in a short period of time, we conclude that they have clear advantages over IELTS in the prediction of international student’s study success.