: This study aims to explore the relationship between syntactic and lexical complexity and also the relationship between different aspects of lexical complexity. To this end, speech monologs of 35 Iranian high-intermediate learners of English on three different tasks (i.e. argumentation, description, and narration) were analyzed for correlations between one measure of syntactic complexity (mean number of clauses per Analysis of Speech Unit) and two measures of lexical complexity (diversity and sophistication). Spearman’s rho was used to calculate correlations between the average scores for syntactic and lexical complexity obtained from the three tasks and also for each of the three tasks individually. The results showed that the average scores for lexical diversity and lexical sophistication correlated positively, but the correlation was found only for the narration task. Also, the average scores for syntactic complexity did not correlate significantly with any of the average scores for the two measures of lexical complexity. However, the pattern of results differed across the three tasks. In the argumentation task, syntactic complexity correlated significantly only with lexical diversity. Syntactic complexity did not correlate significantly with any of the two measures of lexical complexity in the description task. In the case of the narrative task, there was a significant correlation between syntactic complexity and both measures of lexical complexity. The results are discussed in light of Levelt’s (1989) speaking model
