The thermal environment in the schools is associated with the quality of school buildings and correlated to the quality of the learning process. Hence previous studies have been conducted in several countries, but there was still a lack of studies in Indonesia. This study aims to find out thermal environment conditions through long-term measurement. Some schools have been selected which are located in Sumatra and Java Islands. Air temperature, relative humidity, and surface temperature were collected from the loggers that have been installed in every school. The measurement was 7 months sequent from July 2023 until February 2024. This study showed that the outdoor thermal environment in Indonesia is poor in the daytime and relatively good in the nighttime throughout this measurement period. Therefore, it has become clear that ventilation at night has the potential to passively improve the indoor thermal environment.