Nowadays, mind mapping technique as a graphical way of representing ideas has been of growing interest among the educators in many countries, but it has not been paid much attention in Iran in some vital fields of language, especially in the realm of vocabulary teaching and learning. The current study tried to examine whether mind mapping technique has any significant effect on Iranian EFL learners’ depth and breadth of vocabulary. It also investigated the role of gender in the effectiveness of mind mapping on the EFL learners’ depth and breadth of vocabulary. The design of the present study is quantitative quasi- experimental design consisting of a pretest, treatment, experimental and control groups, and a post-test. To conduct the study, 60 out of 80 EFL learners were selected from two language institutes in Sahneh, Kermanshah. Then, they were randomly divided into two equal groups; a control and an experimental group which were basically consisted of both genders. While mind mapping technique was used to teach the experimental group, in control group the participants were taught vocabulary items using traditional procedures such as word lists and translation. The results of the study indicated that mean scores of the learners in experimental group of vocabulary breadth and depth were improved at least by about 5 points while the mean of those in the control group increased by 2.5 points. Thus, the learners’ significant improvement in both domains of vocabulary in experimental group signifies the effectiveness of mind mapping technique of vocabulary teaching in educational settings. On the other hand, the results revealed that the females’ mean scores of vocabulary depth were significantly better than the males after receiving the treatment while the males’ improvement of vocabulary breadth was better. Based on the findings of the study, applying mind mapping technique in teaching and learning vocabulary can effectively help designers, teachers and students develop creative ideas, stimulate the learners’ minds, help them maintain vocabularies actively for a longer period of time, and have a more sustainable effect on remembering and memorization of newly received vocabularies.
