International Journal of Research Studies in Language Learning 2014 April, Volume 3 Number 2, 17-28 © The Authors / Attribution-NonCommercial-ShareAlike CC BY-NC-SA The relative significance of lexical richness and syntactic complexity as predictors of academic reading performance Karami, Mehdi Azerbaijan Shahid Madani University, Iran (karami_m58@yahoo.com) Salahshoor, Farzad Azerbaijan Shahid Madani University, Iran (farzad.salahshoor@gmail.com) Received: 2 June 2013 Revised: 16 October 2013 Accepted: 17 October 2013 Available Online: 10 November 2013 DOI: 10.5861/ijrsll.2013.477 ISSN: 2243-7754 Online ISSN: 2243-7762 OPEN ACCESS Abstract Reading academic texts that include mainly university textbooks has been a challenge for EAP learners. There are various reasons for text difficulty; however, linguistic elements were investigated in this study. The aim of this study was to determine whether lexical richness of the readers would be a more potent predictor of their academic reading performance or their ability for producing and processing complex syntactic structures. The study involved 50 ELT teacher trainees, 25 juniors and 25 seniors, at Shahid Madani University of Azerbaijan, Iran. In a standard multiple regression design, the participants were given an opinion essay-writing task and an IELTS academic reading test. Their scores on IELTS academic reading test were regressed against LFP (Lexical Frequency Profile) and MLTU (Mean Length of T-Unit) indexes of their essays. LFP index is a measure of lexical richness adapted to the web for free online access under the name Web-VocabProfile, and MLTU index is a measure of syntactic complexity. Results indicated that the ability in producing and processing complex syntactic structures rather than mere grammatical knowledge can be considered as effective a predictor of academic reading comprehension as lexical richness. Therefore, lexical richness may no longer be supposed as the single most important predictor of academic reading performance. Keywords: academic reading performance; syntactic complexity; MLTU; lexical richness; Web-Vocab Profile