Abstract: This article reports the results of a study on the effects of pre-task planning and on-line planning on L2 written linguistic performance in timed writing. 120 Chinese university non-English majors of two different L2 proficiency levels participated in the study. Their written texts were coded and analyzed in terms of fluency, accuracy and complexity. Results showed that pre-task planning improved the learners’ fluency significantly while a little with accuracy and

syntactic complexity. On-line planning helped to improve the learners’ lexical complexity, but not to a large extent. There was no interaction between planning style and L2 proficiency affecting fluency and accuracy, but the interaction could be observed in terms of both syntactic complexity and lexical complexity, which indicated that learners of high L2 proficiency benefited from pre-task planning in complexity while learners of low L2 proficiency did not.