This study links the agency lens with the intercultural engagement of international students and examines how agency is affecting and is affected by the church participation (rather than other social engagement within universities) of non-Christian Chinese students in the UK. Adopting agency and adaptation theories, this research analyses quantitative data from questionnaires answered by 501 Chinese students and qualitative data from interviews with 15 students. The result shows that agency offers a critical perspective in terms of cross-cultural engagement for international students, and it complements a broader approach to understanding adaptation and self-formation in cross-border educational experiences. The research proposes a new theory, Theory of Agentive Cross-cultural Adaptation, and highlights the changes in agency and reflexivity modes throughout students' international educational journeys whereby they actively respond to their own individual needs, address their problematic situations, and construct their personal intercultural spaces both within and beyond the university campus. In particular, Chinese students managed the different modes of relationships based on church experience and negotiated the identity paradox between "cultural interpreters" and "believers" in terms of their understanding of Christianity. The study encourages universities to facilitate spaces of intercultural engagement for international students to exercise their agency within the university and wider social contexts.