The practice of occupational therapy (OT) has been extended to include not only a hospital-based but also school-based setting. School-based occupational therapists (SBOTs) work as health professionals in an educational team that provides a transition service in special education schools, and encourages students to meet their goals and become potential learners. The objective of this study was to explore the current situation of the OT service for students with disabilities in special education schools during their transitional periods. This study had a qualitative approach. The participants comprised six SBOTs in special education schools in Chiang Mai province, Thailand. The research instrument consisted of semi-structured interviews with open-ended questions. Thematic analysis was conducted in steps of data analysis. The results found ten categories in four themes as follows. The first theme of roles and involvement of occupational therapists (OTs) had two categories: formal roles and involvement and informal collaboration. The second theme of OT service for transition had two categories: types of intervention programs and timing in providing the OT service. The third theme of barriers against providing the transition service had four categories: informal school policies on the transition service, OT workloads, differences in the background and perspectives of school professionals, and parental involvement. The fourth theme of opinions to decrease the barriers had two categories: explicit educational policies and use of technology as tools for involvement and collaboration. SBOTs provided the transition service in formal and informal collaboration through main and supplementary intervention programs. The findings indicated many barriers. Explicit policy and use of technologies were offered to decrease the barriers against providing the OT service.