A rise of nationalism worldwide presents complex challenges for international schools, which have long been regarded as archetypes of cosmopolitanism in education. In this article, we apply the concept of cosmopolitan nationalism to investigate how interplays between cosmopolitanism and nationalism manifest in practice at international schools. We conducted a multi-site case study of five international high schools in the Pearl Delta River region in Southern China, covering cases in Guangdong Province (Guangzhou and Shenzhen), Hong Kong (two schools), and Macao. Through field observations, website analyses, and interviews (n = 105) with principals, teachers, parents, and students, we provide descriptive snapshots of each case. Three major findings demonstrated a 'tug-of-war' between cosmopolitan and national forces: (1) diversity in how cosmopolitan education is interpreted and implemented, (2) a growing influence of nationalism on educational objectives and practices, and (3) counterbalancing resistance to nationalistic elements grounded in cosmopolitan values. These points are discussed in light of a newly adapted schematic depiction of cosmopolitan nationalism at the school-level. To conclude, we reflect on how a balance of rootedness linked to national belonging, pride, and traditions along with cosmopolitan learning environments that promote openness to the world may represent the future of international schooling.