In line with increasing attention being paid to the role of positive emotions in second language (L2) proficiency and knowledge, this study set out to examine the relationships between domain-specific emotions (L2 grit, language learning curiosity, foreign language enjoyment, and foreign language classroom anxiety) and L2 vocabulary knowledge. To this end, we administered a questionnaire consisting of domain-specific instruments, which purport to measure the target emotions, as well as two widely used L2 vocabulary tests. College students studying English in the South Korean context participated in the study, and they completed both the questionnaire and the vocabulary tests. The results revealed that participants' vocabulary test scores positively correlated with positive emotions, such as a sub-construct of L2 grit (consistency of interest), language learning curiosity, and foreign language enjoyment. In contrast, their scores negatively correlated with negative emotion -- foreign language classroom anxiety. In the regression analysis, it was also found that a sub-construct of L2 grit (consistency of interest) and language learning curiosity were significant predictors for L2 vocabulary knowledge, while controlling for the effects of other variables.