This article reports results of a longitudinal study of vocabulary breadth knowledge growth, vocabulary fluency development, and the relationship between the two. We administered two versions of the Vocabulary Levels Test (VLT; Nation 1983; Nation 1990; Schmitt et al. 2001) to 300 students at a Chinese university at three different time points over 22 months, with an interval of 11 months between each administration. The first version was administered in paper format to estimate participants' vocabulary breadth knowledge, and the second in computer format to assess their speed of meaning recognition. Results indicate a significant effect of frequency level on the rate of vocabulary breadth knowledge growth and vocabulary fluency development as well as a weak relationship between vocabulary breadth knowledge and vocabulary fluency that is affected by frequency level. Findings also suggest that vocabulary fluency development lags behind vocabulary breadth knowledge growth.