Purpose: The purpose of this paper is to explore how financial institutions adopt business process improvement (BPI) for improving service quality, to enhance customer satisfaction. To explain this adoption, it was necessary to develop a theory to explain the linkages between BPI initiatives and customer satisfaction. Design/methodology/approach: Case study was used asthe research strategy, following the theorybuildingprocess suggested by Eisenhardt. In total, three phases of data collection were employed, with expert interviews for theory enhancement and validation. Findings: The authors identified three main stages of BPI adoption. A theory model was developed and refined using the empirical findings, to provide understanding of theoutcomes of BPI initiatives. This model is compared with existing service quality models. Research limitations/implications: The research outcomes represent an extension of existing service quality approaches, to consider the BPI adoption process as well as broader organisational issues. However, data were collected only from Thai financial institutions, which might impact thegeneralisation of the results. Practical implications: The proposed theory model is developed at an operational level, and specifically aims to provide managers with adoption guidance and a practical foundation for further development of operationallevel assessment, assisting a more systematic evaluation of the outcomes of specific BPI initiatives at the project level. Originality/value: The paper provides empirical evidence of BPI adoption in a financial services context. A theory model ispresented based on service quality principles, to help explain BPI adoption outcomes at an operational (e.g. project) level, which provides a different perspective to that of existing service quality models.