The relationship between motivation and EFL proficiency is an issue of great concern in previous research on foreign language learning. However, work in this area offers inconclusive evidence with regard to the directionality of their relations. Using cross-lagged structural equation modeling, this study investigated the directionality of the relations between motivation and EFL proficiency among a sample of 262 Chinese university students (147 female, 115 male). The author adopted a three-wave, longitudinal, cross-lagged panel design and found that changes in instrumental orientation resulted in changes in EFL proficiency throughout the first school year. Changes in integrative orientation were not causally associated with changes in proficiency during the first semester, but the latter predicted the former during the second semester. Changes in motivational intensity predicted changes in proficiency during the first semester, but the relationship became insignificant during the second semester. Theoretical and applied implications were discussed.