The current study investigated the extent to which L2 learners' productive vocabulary knowledge could predict multiple dimensions of spontaneous speech production. A total of 39 English as a foreign language (EFL) participants with varying L2 proficiency levels first completed a productive vocabulary knowledge task (Lex30). Their spontaneous speech, elicited via a series of picture description tasks, was then assessed for comprehensibility (i.e. ease of understanding), accentedness (i.e. linguistic nativelikeness) and fluency (i.e. speech rate). The findings showed that the productive vocabulary scores significantly correlated with L2 fluency, but not with comprehensibility or accentedness. These results suggest that more proficient L2 learners, as measured by productive vocabulary scores, may speak spontaneously with fewer pauses and repetitions, and at a faster tempo. Finally, future research directions are discussed with a focus on the relationships between vocabulary knowledge and speaking.