The current study examined the use of electronic textbooks designed as mobile applications for learning vocabulary in English among Iranian university students. To this end, 95 university students in an experimental (N = 50) and a control group (N = 45) participated in the study. An explanatory sequential mixed methods design was employed and over an academic semester, the participants used either traditional materials or mobile-based electronic textbooks for learning 600 words in English. To assess the outcomes from different learning conditions, receptive knowledge of the target vocabulary items was tested in three junctures of time (i.e. pre-, post-, and delayed post-test). Additionally, open-ended questionnaires and interviews were used to collect qualitative data from the experimental group to further investigate their perceptions of using mobile-based electronic textbooks for vocabulary learning. The findings revealed a significant main effect for time and both groups significantly improved their vocabulary knowledge from pre-test to post-test. Moreover, a significant main effect was found for using electronic textbooks on mobile devices, and the experimental group outperformed the control group on the post- and delayed post-tests. The qualitative findings revealed three perceived benefits, namely "episodic learning," "easy access to materials," and "enhanced enjoyment" for mobile assisted vocabulary learning through electronic textbooks. The perceived challenges were related to "health concerns," "distractions associated with mobile environments," and "external pressure resulting from excessive mobile use" among the participants. In general, the findings of the study shed light on the potential offered by mobile-based textbooks for learning English vocabulary, with implications for teachers and materials developers in language teaching programs.