In 1997, the sovereignty of Hong Kong was returned from Britain to China. Henceforth, Hong Kong was no longer a British colony, but a special administrative region of the People’s Republic of China. Throughout the years during the British governance, English was used as the major medium of instruction (MoI) for secondary education. Regardless of strong public resistance, the mother tongue education policy was implemented in Hong Kong shortly after the political handover. Since then, Cantonese (the local language) replaced English (the ex-colonizer’s language) as the major medium of instruction in mainstream secondary schools. However, the government initiated a ‘fine-tuning’ policy eleven years after, which allows a more extensive use of English in Hong Kong classrooms. Under such a critical period of change, this study was conducted to examine the impacts of the new policy on students’ learning motivation and achievement. This paper reports the results gathered from a questionnaire survey collected from 100 students and interviews with four experienced teachers, through which, the ‘fine-tuning’ MoI policy is evaluated.