The current study aimed at investigating the effectiveness of the e-mind map strategy in the instruction of grammatical and lexical competences in developing the second-year preparatory stage students' EFL writing skills. To achieve the purpose of the study, two instruments were used: a questionnaire to determine the writing skills appropriate to the participants, a pre-post EFL writing test with an analytic scoring rubric to assess the students' performance in descriptive writing and writing emails after checking its validity and reliability. The current study adopted the quasi-experimental method (the pre- test posttest equivalent- groups design). The participants of the study consisted of sixty students in Monshaat Boleen Preparatory/ Secondary Institute for Girls in Al Behira Zone. Two intact groups were randomly assigned to an experimental and a control group. Thirty students represented the experimental group, and thirty other students represented the control group. Results of the study revealed significant differences between the mean scores of the post administration of the two groups in favor of the experimental group. According to the statistical analysis of testing the hypotheses, it can be concluded that the electronic mind mapping strategy used has had a positive impact on developing the writing skills of the second-year preparatory students' EFL writing skills. The researcher observed clear progress in the female students' responses in the writing test.