Ever since the transfer of sovereignty over Hong Kong from the United Kingdom to the People’s Republic of China on 1 July 1997, policy makers in Hong Kong have instituted a series of de-colonising language policies, notably Mother Tongue Education (Education Department, 1997. Medium of instruction guidance for secondary schools. Retrieved from https://www.legco.gov.hk/yr97-98/english/panels/ed/papers/ed1508-6.htm.) which emphasises the importance of the Chinese language in rebranding the city as a cosmopolitan bilingual city in Asia. One unintended consequence is that linguistically and culturally diverse pupils in the system are struggling to learning Chinese as an additional language (CAL). Against the backdrop of existing CAL policies which promote decentralisation and school-based curricula, this exploratory paper aims at examining the extent to which the language planning context has facilitated and constrained CAL teachers’ agency in Hong Kong secondary schools. Based on in-depth, semi-structured interviews with 10 CAL teachers purposively recruited from three local secondary schools, this study finds that certain features of the language planning contexts have constrained and transformed teacher agency in ways that lead to what Cummins’s (2000. Language, Power and Pedagogy: Bilingual Children in the Crossfire. Clevedon, UK: Multilingual Matters.) refers to as ‘the narrowing of the curriculum brought about by teaching to the test’ (p.248). The resultant emphasis on the short-term CAL goals, as manifested by this maximum-variation sample of teachers, is discussed with attention to how teacher agency is ecologically achieved and claimed, and a call for restructuring existing CAL policies to attend more to the mediating impact of the ecology on teacher agency, and to purposively channel teachers’ agentive action towards the long-term goal of mainstreaming. In doing so, CAL teachers can truly be ecologically set up as agentive language planners in the face of increasing