In building refurbishment projects, dynamic building simulation is popularly used to predict the energy saving potential of various refurbishment scenarios.However, in this process, it is not clear whether occupant behaviour should be carefully modelled due to the lack of evidence about its impact on the prediction results. To answer this question, this study selected an UK public building and used dynamic building simulation to predict the energy saving potential of common refurbishment measures, under various occupant behavioural conditions. The results revealed that for the case study building occupants' heating behaviour has a significant impact on the predicted energy saving potential of all evaluated refurbishment measures: when changing from passive heating users to active heating users, the energy saving potential was nearly doubled. Although occupants' window opening behaviour was not shown to be as important as heating behaviour for the refurbishment of the case study building, it has a specific influence on the refurbishment measure of increasing window layers: when windows are opened longer, the effectiveness of increasing window layers on promoting the building energy efficiency is decreased. According to the findings from this study, occupant behaviour should be considered as an important aspect in building refurbishment projects.