Mainland Chinese students (MCSs) represent the largest non-local student group in Hong Kong and their adaptation experiences require more research attention than exists. This study investigates MCSs’ psychological adaptation to Hong Kong with a language and social psychological approach by invoking Communication Accommodation Theory (CAT) and Willingness to Communicate in a Second Language (L2 WTC). Survey results were collected from 372 MCSs studying in Hong Kong. Structural equation modelling yielded an empirical model that describes the relations between MCSs’ perceived Cantonese competence, Cantonese use anxiety, Cantonese confidence, WTC with locals in Cantonese (Cantonese WTC), accommodative encounters and contact with locals, acculturative stress, and psychological adaptation. The model highlights the focal role of MCSs’ frequency of accommodative encounters with locals and Cantonese use anxiety in their Cantonese WTC, which underscores the situational factors (i.e. an accommodative conversational partner) in an individual’s L2 WTC. This study offers valuable insights into MCSs’ adaptation to Hong Kong from an intergroup communication perspective and provides novel theoretical contributions by empirically examining the transferability of L2 WTC to an eastern cultural context and to languages other than English as well as the simultaneous application of CAT and L2 WTC to better account for intergroup communication.