The current study investigated the usage of the bilingual Vocabulary Size Test (VST) within Korean EFL environment. Thirty-two university students with an intermediate to high proficiency participated in this study. The students were given a Korean bilingual version of VST and reported their official English scores. The findings of this study are as following: (1) The VST scores showed a significant relationship with students’ proficiency scores which indicates that students with a bigger size of vocabulary had a higher proficiency of English. (2) When VST scores were divided into each frequency level, no particular frequency band demonstrated a significant relationship with English proficiency. Also, the difficulty of each level did not show a consistent pattern. Based on the results of VST, the influence of Korean EFL environment such as loanwords and the test-oriented education system was discovered. This study provides implications for teaching vocabulary in EFL environment and suggests the need for developing of a vocabulary size test for Korean context.