In recent years, the demands for effectiveness and evidence in social work have increased in all work areas, including that of healthcare. This has sparked the discussion on concepts such as practical- and theoretical knowledge and their respective roles in social work. In the light of this, the purpose of this candidate thesis is to investigate healthcare social workers understanding of practical- and theoretical knowledge in the working process as well as their respective influence and importance. This candidate thesis is based on three interviews with social workers from different departments in Norrlands Universitetssjukhus in Umeå, Sweden. To provide range to the thesis, the interviewees were chosen from a purposeful sampling. The data was examined by using conventional content analysis. A range of theories were identified as tools of theoretical knowledge and was said to develop mostly from studies and tutoring. The relationship competence, that is the ability to create a trusting and secure relationship with the patient, was referred to as practical knowledge which typically came with work experience. Both types of knowledge in the work process were perceived as important but were described as having different roles. Namely, the knowledge competence was perceived from a practical knowledge base with theory as a guiding tool in the continuous working process. Furthermore, there were some difficulties in distinguishing both types of knowledge from either the working progress or each other which entails the need of further research.