Based on the quantitative analysis of L2 English texts from Korean undergraduates, the present paper demonstrates the possibility of distinguishing L2 speaking proficiency with differing measures of syntactic complexity in English writing. To this end, 14 measures of complexity were gauged using an L2 Syntactic Analyzer (Lu, 2010) in 89 EFL essays from a learner corpus to find out the best indicators of L2 speaking proficiency. As a result of the normality assumption test, the logistic regression analysis was applied and the model was significant in classification according to L2 proficiency and the classification was correct in 62.9% of the studied cases. Furthermore, it showed that the best predictor of L2 speaking proficiency was the complex nominal per T-unit (CNT). Specifically, upon the acquisition of CNT, EFL learners are 6.4 times more likely to achieve higher proficiency in speaking English. Taken together, this paper suggests that EFL students' quality of writing can be effectively used to distinguish their speaking ability.