Microfinance Institutions (MFIs) play important roles in socio-economic development and poverty alleviation particularly in developing countries. It has however been argued that the focus of MFIs is changing from the traditional purely social to commercial (mission drift) and has been criticised for neglecting the welfare of citizens and grassroots accountability in favour of commercialisation and accountability to donors/shareholders. This mission drift has resulted in changes in the structure and practices of MFIs. The study has been designed to examine how the accounting and accountability practices of a MFI can change in response to changes in its mission. The study presents case evidence from a large MFI operating in Cameroon with data collected through semi-structured interviews, informal discussions and documents. The study traces the evolution of the organisation and its accounting and accountability practices. A theoretical framework of an interpretive nature is used which draws on institutional entrepreneurship theory in order to highlight the importance of actors in the change process. The findings suggest a mission drift and transformations over the years from a social to a commercial organisation with the change impacting significantly on its structure and accounting and accountability practices.