a growing body of research has indicated that students of esl/efl are reticent and unwilling to be engaged in oral activities in english lessons. communicative language ability includes speaking ability, so vocabulary knowledge plays an integral role in speaking a language. however, there have been few studies examining the degree to which vocabulary knowledge affects speaking ability. the present study aimed to explore the degree of reticence in iranian efl learners and to find out the roles that productive vocabulary knowledge and gender may play in their reticence. to accomplish this, 56 male and female english language learners participated in the study. unwillingness-to-communicate scale and vocabulary-size test of controlled productive ability were used. to analyze the data, descriptive statistics, pearson product-moment correlation and an independent t-test were used. results of the study revealed a relatively low level of reticence among iranian efl learners. however, it seems that learners mostly avoid communication rather than have a negative attitude toward class participation. in addition, it was found that the learners’ vocabulary knowledge had a significant relationship with their reticence; while, no significant difference was found between iranian male and female learners in terms of reticence.