This paper examined factors affecting Korean EFL learners’ word association types in their L2 mental lexicon. Specifically, vocabulary size of the learners was examined to see if it had any significant relationship with word association types. To this end, experiment procedures that included vocabulary size test and the lexical decision task as well as the word association task were conducted on 40 Korean EFL learners. Reaction time and accuracy of responding to word associations in the lexical decision task were measured. Subsequently, a correlation analysis was conducted with their vocabulary size. Additionally, learners’ word association types were analyzed based on the results of word association task. The results showed that Korean EFL learners’ vocabulary size had significant correlations with their accuracy in identifying syntagmatic and paradigmatic associations, but not in the phonological association. However, their accuracy was not correlated with reaction times. The results indicate that L2 learners’ mental lexicon is partially dependent on their vocabulary size of the target language, and it is variable depending on word association types.

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.