The ever-expanding boundary of knowledge for social work practice confronts social work practitioners with a great variety of theories and approaches which are incommensurable with each other and esoteric that renders the relationship between social work knowledge and practice problematic. To resolve this epistemological issue, proponents of the 'scientific designer-practitioner model' advocate production of scientifically proven intervention approaches for social workers' application to practice. However, the adherents of 'heuristic perspective on social work' pinpoint that the actual social work practice situations are too complex and indefinite to be. covered by codified knowledge; instead, they maintain that social workers should think like a researcher to produce and use their own practice theory/wisdom (knowledge construction) through generating and testing hypotheses in the course of intervention. Through the 'practice perspective on social work', I criticize them of misplacing emphasis on practitioners' cognitive process as to knowledge construction within intervention and suggest to investigate the infrastructure of knowledge co-construction by both social workers and service users within intervention conversation. Through the lens of conversation analysis, six transcribed interviews between social workers and their service users have been closely examined. The core epistemic activities (episactivities), some elementary conversational actions (episgears) of knowledge co-construction and some of the strategies (epistechniques) employed by social workers to handle hurdles (episbottlenecks) arising in the process of knowledge co-construction are identified. These findings imply a new set of basic conversational skills for social work which may contribute to the resolution of the epistemological issue of social work. I term them 'epistemically informed intervention'.