Case management of Persons with Disabilities (PWD) particularly the mental category has been scarcely studied in Malaysia. With mental illness rapidly growing into a public health issue, more research especially in the aspects of case management is needed. In relation to that, this paper aimed to explore on the challenges in case management that case workers for persons with mental disabilities (PWMD) faced in Malaysia. This qualitative study conducts in-depth interviews twice with 10 case workers from Medical Social Work Department and Social Welfare Department. Data were analysed thematically using content analysis method. The study discovered that challenges arise were negative perception towards PWMD, lack of specialized trainings, and lack of effective collaborations between agencies. The findings suggest that the Health Ministry and Welfare Department should enhance collaboration between them in getting their resources such as information and manpower together in fulfilling the needs of PWMD. On top of that, the study highlights the importance of case workers’ roles in brokering between the agencies in order to increase client functionality in society. This paper is important for policy makers to take into account the needs and the capacity of the PWMD and also caseworkers to ensure the effectiveness of both welfare and health services. Thus, the case management services for persons with mental disabilities will be improved which are aligned with Malaysia’s social work competency standards.