Breast cancer (BC) is the most common type of cancer among Malaysian women with reported incidence increased in trend according to data from 2012 to 2016 [1]. Moreover, compared to the data from 2007 until 2011 and 2012 until 2016, Malaysian women are more likely to present with late-stage BC [1]. Breast self-examination (BSE) was found to be more effective when combined with a mobile app intervention in promoting early detection [2]. Even though smartphone app users were increasing, there is a lack of culturally appropriate content, health providers’ support and accessibility to reliable information [3]. The objective of this study was to develop BrAware, a breast awareness mobile app based on the Health Belief Model (HBM) and evaluate the effectiveness of BrAware for health education and promotion. The HBM-based requirement analysis was used to develop BrAware, which includes elements including the risk factors infographic, survival statistics, BSE video, reminders, support groups and ‘myths and facts’ content. An approval from the Human Research Ethics Committee (HREC) Universiti Sains Malaysia was obtained (USM/JEPeM/18080380) prior to data collection. A quasi-experimental pre and post-test research design were conducted from 1st October until 1st December 2021. The recruitment of participants was done through media social platforms such as the Facebook page of ‘Penduduk Kota Bharu’ and the WhatsApp group. It utilized an online survey using an adapted Bahasa Malaysia version of the Breast Cancer Awareness Measurement Tool (B-CAM) [4]. The post-test was administered after the participants were familiar with and used BrAware for two months. The data analysis was done using the Statistical Package for Social Sciences (SPSS) version 26.0. The raw scores of knowledge were summed up to 100% with a high score indicating high knowledge. A paired t-test was used to analyze the effectiveness of BrAware on knowledge in BC and BSE. The null hypothesis was rejected if the p-value is