In this article we consider the issues and problems asseen by Hong Kong teachers during the transitional period fromEnglish to mother-tongue Chinese as medium of instruction (MOI).It is vital to examine teachers' perceptions for they reflect thereal situation at the school level and are likely to affect thesuccessful implementation of MOI policy. Our data show that whileteachers generally adopted a positive attitude towards thechange, they experienced difficulties, such as lack of confidenceusing Modern Standard Written Chinese (MSWC) as a teachinglanguage, lack of quality Chinese teaching resources, pressureresulting from parents' resistance and anxiety on account of theuncertainty of government language policy for the seniorsecondary level.