This study explored the contribution of second language (L2) discipline-specific vocabulary to Chinese chemistry major undergraduates' reading of textbooks. Participants included 82 second-year undergraduates majoring in chemistry. Their discipline-specific vocabulary knowledge and chemistry textbook reading ability were measured. Their L2 proficiency and chemistry knowledge data were collected. Correlation and multiple regression analyses revealed that discipline-specific vocabulary was highly correlated with L2 proficiency and disciplinary knowledge, and discipline-specific vocabulary contributed the most to textbook reading, bigger than either L2 proficiency or disciplinary knowledge. Implications for discipline-specific vocabulary and English for academic purposes (EAP) reading instructions are discussed.