This study investigated the relationship between the English vocabulary size of first language Cantonese speakers in Macau (N=77) and engagement in extramural English activities. The 140-item Vocabulary Size Test was used to collect data on participants’ vocabulary size and a 13-item questionnaire tapped into background learning experiences as well as participation in 16 extramural activities. Small correlations between vocabulary size and book reading, subtitled television viewing, non-subtitled online video viewing, level of education, study abroad experience, and travel abroad experience were found. A medium correlation between vocabulary size and language of instruction in secondary school was also found. A four variable sequential regression accounted for 26% of the variance in participants’ vocabulary sizes, with book reading adding the most explanatory power after language of instruction in secondary school had been eliminated. The impact of extramural activities on vocabulary size and pedagogical implications for the Macau and similar contexts were discussed.