This study examines how hospital social workers (HSWs) in China negotiate professional jurisdiction as healthcare reforms reconfigure interprofessional roles. Drawing on Abbott’s theory of professional jurisdiction and Langley et al.’s boundary-work typology, we conducted a 12-month ethnography in a tertiary hospital in Shanghai and analysed the data using constructivist grounded theory. The analysis identified two boundary strategies: detaching and advocating. Through detaching, HSWs built trust by assuming coordination tasks that other team members struggled to sustain. Through advocating, they deployed professional narratives to explain what social work could contribute and to make its expertise more recognizable to clinicians. Together, these strategies enabled incremental jurisdictional gains and more reciprocal partnerships. These gains, however, were constrained by ‘jurisdictional saturation’, a point where social workers’ ability to expand their roles stalls due to inadequate staffing support or external welfare resources. The concept identifies a paradox of state-led professionalization: policy recognition may extend faster than the resources needed to support practice. The study extends processual accounts of professional jurisdiction by highlighting how jurisdictional change is accomplished through everyday resource exchanges, with implications for hospital social work in other resource-constrained health systems.