IntroductionFemale sex workers (FSWs) experience heightened vulnerability to HIV and other health harms, and cross-border FSWs face additional challenges due to language issues, higher mobility, and weaker negotiation skills. Given the critical role of social network factors in HIV transmission, it is imperative to explore the social network characteristics of Vietnamese cross-border FSWs in China to enhance AIDS prevention and control.MethodsWe conducted semi-structured interviews with 22 Vietnamese FSWs in Hekou County, Yunnan Province from May to July 2018. The samples were selected using a purposive sampling strategy and stopped when reached theoretical saturation. Data collection and analysis were conducted iteratively to identify themes within the data. Participants reported their social relationships and how these relationships affected their HIV risk behaviours. All the interviews were recorded, transcribed verbatim, and reviewed. Thematic analysis was used to analyse the data.ResultsAmong 22 Vietnamese FSWs, the median age was 23.5. Concerning social networks, interviews revealed that their social networks were composed of three components: Workplace networks (customer, boss, colleague), Hometown networks (spouse or boyfriend, family member, fellow villager), and Social institutions networks (Chinese social institutions network, Vietnamese social institutions network). None of these networks can simply support or hinder Vietnamese FSWs’ preventive high-risk HIV behaviours, and the impact is achieved through each network’s ways. Within the workplace network, the predominant influence is the ascendancy-submissiveness dynamic that exists among customers, bosses, and VFSWs. In the hometown network, familial responsibilities emerge as the principal factor impacting VFSWs. Meanwhile, within the social institution network, pivotal roles are played by the Chinese CDC and the Vietnamese government in the dissemination of HIV knowledge.ConclusionsThe social networks of Vietnamese female sex workers exert a dual impact on high-risk HIV behaviors. Interventions should be designed and tailored to address the specific contextual factors and challenges associated with social networks among cross-border FSWs in China and other similar settings.