This research investigated the effectiveness of group work (GW) in EFL vocabulary learning by second . year, non-English major, university students in Taiwan, in comparison with working individually (IW). It also sought to find out students' attitudes towards vocabulary learning in each mode. The context was vocabulary-focused tasks following reading comprehension. In order to gather in-depth information about the process of, vocabulary discovery and retention and students' attitude to learning vocabulary through these two modes, questionnaires (44 students) and interviews (24 students) were used, along with vocabulary knowledge tests to measure knowledge gains (44 students). The design was repeated measures. Findings showed that students' overall improvement in vocabulary knowledge with GW was higher than that with IW. The results inferred from participants' statements in interviews and choices on the questionnaires showed that students' discovery of word knowledge in GW was greater than that in IW mainly because of having more opportunities to give and receive word knowledge from group members. Their retention of word knowledge in GW was a little higher than in IW because of giving and receiving helps during group discussion and learning in a friendly environment. Moreover, working with different group members in each GW. activity . seemed to affect their construction of groups (e.g. communicating about the tasks, assigning roles). Finally, students' attitude towards learning vocabulary through GW and IW changed. They favoured learning vocabulary through GW rather than IW less after GW was implemented, even though their vocabulary learning was improved. Pedagogical implications drawn from our findings were twofold for the educational authorities, English department, and teachers in Taiwan. First, the use of group work needed be encouraged in English class in secondary school and university. Second, provision of a vocabulary learning course at university and emphasis vocabulary learning in the university reading class were needed.