lexical diversity of argumentative and narrative writings of L2 learners, and the contribution of syntactic complexity and lexical diversity to the writing quality in the L2 argumentative and narrative writings of EFL learners. To this end, 46 pre-intermediate and intermediate Iranian EFL learners from four intact classes wrote one argumentative and one narrative essay in L2, and one argumentative and one narrative essay in L1 on different topics. Paired-samples t-tests revealed that lexical diversity surfaced more in the L1 writing of the learners. Multiple linear regressions indicated that among five measures of syntactic complexity, mean length of T-unit and clauses per T-unit better predict the quality of argumentative writing. In addition, complex nominals per clause are better predictors of narrative writing quality. Simple linear regressions showed that lexical diversity is a significant predictor of L2 writing in both genres. Based on the findings, writing instructors are advised to provide L2 learners with explicit instruction on the use of diverse vocabulary and different syntactic structures in order to help them improve the quality of their writing.
