The thermal performance of an educational office building which exhibits sustainable design principles of passive architecture (emphasis on the use of natural ventilation) was studied. The main aim of the study was to investigate the thermal conditions, ventilation possibilities and preference for office type in the building. The building has individual cell and open-plan office spaces with different orientation and ventilation possibilities (cross, one-sided and borrowed ventilation). Data loggers were installed to monitor the environmental conditions existing in the building during the rainy season. The evaluated data showed that the indoor temperatures were comfortable (mean of 25°C), the relative humidity values were mostly high (80 - 85%) and the dew point temperature (22°C) was found to be close to the recommended minimum comfort temperature. Moreover, the enclosed corridor space was found to be warmer than the adjacent office spaces during the day time. The use of cool night air as a passive cooling strategy is recommended. Preference for office types with ventilation possibilities could not be statistically recommended since all the evaluated thermal values showed insignificant deviations.