Mohammad Ali Heidari-Shahreza, The Effect of L1-L2 Lexicalization Mismatch on Incidental Acquisition of Receptive Vocabulary Knowledge, Volume 39, International Letters of Social and Humanistic Sciences (Volume 39) https://www.scipress.com/ILSHS.39.67 Abstract: The researcher was interested to explore the possible effects of L1-L2 lexicalization mismatch on the acquisition and retention of receptive vocabulary knowledge by 90 Persian-speaking EFL learners. Lexicalization mismatch was defined in the context of this study as the lack of a lexically equivalent translation in learners’ L1 (i.e. Persian) for an L2 word (i.e. English). Thus, non-lexicalized words referred to those L2 words that required a longer string of L1 words to cover their essential semantic features. The findings indicated that there were significant differences between lexicalized and non-lexicalized target words in the receptive knowledge of meaning and form and receptive knowledge of associations. Thus, it seems non-lexicalized words are most likely to cause extra difficulty for EFL learners in the semantic aspects of vocabulary knowledge. Using enhanced input within a systematic vocabulary recycling program is recommended to deal with such words. Keywords: Incidental Vocabulary Acquisition, L1 Translation, Lexicalization Mismatch, Persian-Speaking EFL Learners