The use of 'chunks' is not only a common and characteristic feature of first language use, but may also be a distinguishing factor between less and more proficient second language users. The present study aimed at investigating potential correlations between chunk use and holistically rated proficiency scores and development over time in advanced Chinese learners of English as a second language (L2) over the course of 18 months of English classes. Neither holistically rated proficiency scores nor common complexity measures had shown any progress in these learners, but a few lexically based measures did. Therefore, the development of chunks in these learners was examined as chunks are mostly lexical in nature and might show more subtle progress over time. The use of chunks was examined in the first and last two texts of the learners and, in line with previous research, it was found that more proficient writers use relatively more chunks, specifically collocations. Chunk coverage, the total number of chunk words divided by the total number of words, also correlated with some holistic proficiency scores, and increased significantly over time. Average chunk length did not show any correlation with proficiency scores nor did it increase over time. Increased proficiency in written texts is thus specifically related to the use of more chunks. This study shows that development in advanced Chinese L2 learners of English appears to be subtle, which might be due to the fact that at this advanced level mainly lexical changes take place. Future research into development over time in advanced learners may thus have to zoom in on lexical measures especially. Implications of this study point to the importance of promoting the use of target language chunks to advanced learners of English.