The decision support system (DSS) provides systematic data for improving effective decision-making by school-based occupational therapists (SBOTs) in healthcare services. The purposes of this study were to develop the DSS and investigate its usability in providing the occupational therapy (OT) service for students with disabilities during transition periods. This study was conducted by using the Research and Development (R&D) design. There were two phases of methodology. Phase I explored the needs of SBOTs regarding DSS development. Six SBOTs were appointed for their opinions by in-depth interview with semi-structured questions. Content analysis was conducted in this phase. Phase II investigated usability of the DSS in providing the OT service to students with disabilities during transition periods. The participants comprised 18 SBOTs and 18 teachers, who worked together in providing educational programs for students with disabilities. The System Usability Scale (SUS) was used for investigating efficiency of the web-based DSS. Results found that the web-based DSS comprised two main parts of content and three main functions. In terms of content, the web-based DSS included personal and OT service information. In terms of function, syncing information from the Special Education Technology (SET) software program, making decisions on OT intervention programs and sharing OT service information were included. The SUS was used for investigating usability of the web-based DSS. The SUS score was 72.98, which indicated good usability. These findings indicated that the web-based DSS was meant to support decisions made by the SBOTs in providing OT intervention for students with disabilities during transition periods. In addition, it could be a collaborative tool, which supports sharing student information between SBOTs, teachers and other professionals in preparation for transition planning before moving to higher education levels.