In order to provide evidence to support decision making on the introduction of natural ventilation in the higher education sector in hot-humid climates, this pilot study investigated the relationships between thermal conditions and perceived learning performance (PLP), comparing air-conditioned (AC) and natural-ventilated (NV) environments. A questionnaire survey of PLP and thermal comfort was conducted in four typical lecture rooms in a Thai university (354 responses: AC: NV = 287: 67). The overall environmental comfort in NV cases was found to be greatly influenced by thermal and IAQ perceptions. Thermal perception was a more useful PLP indicator than measured temperature. The PLP of students who reported to be ‘uncomfortable’ was higher (? = 0.021) in the AC than in the NV group. Due to a limited sample size, it cannot be excluded that students in the ‘comfortable’ group may have the same PLP regardless of thermal operating modes. However, this study suggests that the introduction of NV in existing AC environments may negatively affect students’ performance.