The present study investigates the relationship between vocabulary size and writing. This study employed 240 university students. Mochizuki's VST (1998) is used for examining the vocabulary size, and the writings are evaluated using the EFL Composition Profile (Nakanishi, 2006). The results indicate that the relationship between vocabulary size and writing scores can group learners into three categories: (1) 2500 and under vocabulary size; (2) 2501 to 4500 vocabulary size; and (3) 4501 and over vocabulary size. Students in category (1) get low scores in language use and mechanics in general, which means they lack accuracy with grammar and vocabulary in writing. Students in category (2) are in the gray zone where scores depend on the individual. Students in category (3) improve significantly in their writing scores for every item compared to learners whose vocabulary size is 4001 to 4500.
