Mathematics remains one of the most challenging subjects for lower secondary students in Malaysia, particularly in geometry topics such as perimeter and area. Traditional instructional methods often fail to address students’ misconceptions and declining engagement. This study aimed to develop and evaluate eMI-PERLU, an interactive e-module designed to support Form One students’ mastery of perimeter and area by incorporating visual, interactive, and self-paced learning features. A Development Research Design (DRD) guided by the ADDIE model was employed. The population consisted of 266 Form One students at Sekolah Menengah Kebangsaan Tandek, Kota Marudu, Sabah, from which 40 were selected using convenience sampling. Research instruments included expert validity questionnaires and student usability questionnaires, both based on a four-point Likert scale. Data analysis involved Content Validity Index (CVI), expert agreement percentages, Cronbach’s Alpha for reliability, and descriptive statistics for usability. Findings indicated excellent validity, with a CVI score of 1.00 and expert agreement at 96.43%. The e-module also demonstrated good reliability (Cronbach’s Alpha = 0.848). Usability analysis revealed high ratings for usefulness (M = 3.69, SD = 0.47), ease of use (M = 3.70, SD = 0.49), and satisfaction (M = 3.76, SD = 0.46). Overall, eMI-PERLU is a valid, reliable, and user-friendly resource that enhances student engagement and conceptual understanding. The study contributes to advancing interactive mathematics education and offers implications for teachers, students, and policymakers within the Malaysian education system.