The present article reports on the results of a study designed to investigate the effects of two types of lexical modification i.e., lexical simplification and elaboration, on incidental vocabulary acquisition of Iranian EFL learners.To this end, four versions of experimental texts containing 20 target words were created: baseline and simplified versions, as well as elaborated version with two types, i.e., parenthetical elaborated and non-parenthetical elaborated version. ANOVA and Post Hoc analysis were run in order to analyze data obtained from 80 EFL students. Results of two immediate surprise tests, i.e., form recognition test and meaning production test measuring incidental vocabulary learning from modified target words revealed that (a) lexical simplification did not result in incidental vocabulary acquisition (b) both parenthetical and non-parenthetical elaboration were conducive to incidental vocabulary acquisition and (c) comparatively, parenthetical elaborated group outperformed non-parenthetical elaborated group on two incidental vocabulary measures.