The objective of this study is to acquire basic architectural and operational data of gymnasiums of public schools to determine the most effective renovation method that satisfies the criteria of both budget and thermal comfort. In this study, firstly, gymnasiums of 64 elementary schools in the S-ward of Tokyo are architecturally characterized. The result of this characterization indicates that the building forms of the gymnasiums are classified into three types- (1) single-level type, (2) multi-level type, and (3) rooftop pool type. Secondly, an actual field survey is conducted from fall of 2015 to winter of 2016 at three gymnasiums in the S-ward of Tokyo, which are regarded to have distinct thermal environmental characters as determined from the classification results. Accordingly, it is revealed that the air temperature is consistently higher in the multi-level type gymnasiums in comparison to the single-level type. Further, the air temperature is most stable for the rooftop pool type gymnasium.