In bilingual education programmes, teachers, particularly content subject teachers, play an important role in helping students master content knowledge and the target language simultaneously. In this regard, teachers' language awareness, which will affect their pedagogical practices, is crucial. Collaboration between content subject and language teachers is argued to be effective in enhancing teachers' language awareness and strategies of integrating content and language teaching. This study explored this by investigating 12 secondary schools in Hong Kong which implemented partial or full English Medium Instruction, with a specific focus on how cross-curricular collaboration was implemented, and whether this may have promoted teachers' language awareness and practices. With questionnaires, interviews, classroom observations and artefacts, the study observed that teachers were generally aware of the difficulties students encountered when learning content subjects through English, and content subject teachers tended to recognise their roles of incorporating language teaching into content lessons. Such self-reported language awareness was corroborated by the various strategies integrating content and language teaching in the observed ­lessons. These findings demonstrate a cyclic relationship between cross-curricular collaboration and teachers' language awareness -- teachers' language awareness is essential to make cross-curricular collaboration happen, and it is further reinforced after teachers collaborate with each other.