As a response to the advancement of technology into every aspect of human life especially education and the need for more involvement on the side of learners advocated by learner-centered approaches towards education, this study aimed at investigating comparative effect of project-based (PBL) learning and electronic project-based learning (EPBL) on Iranian intermediate English as a Foreign Language learners' idiom learning and retention. 90 male and female participants' were assigned into three groups of control, PBL and EPBL. At the onset of the study, a pre-test of English idiom knowledge was conducted. After 15 sessions of treatment on the basis of specific lesson plan and procedure, learners' knowledge of idioms was measured on posttest and delayed posttests. The results of multivariate analysis of variance indicated that both PBL and EPBL outperformed control group in learning and retention and PBL outperformed EPBL in retention and sustainability of the knowledge. The student's perceived efficacy of PBL in two modes was analyzed using portfolio writing. Theme elicitation analysis suggested that the centrality of the role of instructors, environmental support and traditional education conventions and culture need to be revisited when it comes to implementation of technology in education.