Abstract：Abstract: This article reports an empirical study of the effects of individual output, collaborative output and reading input on second language vocabulary acquisition. Participants were 120 Chinese university non-English majors. They were divided into four groups to complete three different tasks respectively: an individual output task, a collaborative output task and a reading input task. Collaborative output was further divided into writers and non-writers according to different task roles. All four groups took a nine-section multidimensional posttest immediately and a delayed posttest two weeks later. Posttest results revealed that individual output led to significantly more vocabulary acquisition and retention, followed by collaborative writers, reading input and collaborative non-writers respectively. Significant difference in vocabulary learning existed between every two groups, except for that between collaborative writers and reading input. The findings indicate that output induces significant vocabulary acquisition whereas interaction adequacy and task roles determine the effects of collaboration upon learning
