Between 2017 and 2018, we conducted a longitudinal field experiment in a mixed-mode ventilation building located in Wollongong Australia, with a particular focus on occupant thermal comfort and adaptive behaviour. This study investigated how different building operation modes i.e. air-conditioning (AC) and natural ventilation (NV), can have an impact on occupant perception of thermal comfort. Time-And-place matching of objective (physically measured indoor climate parameters, outdoor meteorological data, and building operational information) and subjective data (i.e. occupant survey questionnaires) enabled empirical investigation of the relationships between those parameters. The result of the analysis revealed that subjective perception of indoor thermal environment can be affected by different modes of building operation. Occupants were found to be more tolerant of, or adaptive to, the indoor thermal conditions when the building was in the NV mode of operation compared to the AC operational mode. The applicability of the adaptive comfort standard to the mixed-mode ventilation context was also discussed.