The indoor environment of lecture rooms in universities can affect the learning of students. Nevertheless, study on the actual conditions of air in relation to indoor air quality is rare. This paper presents a case study on the indoor comfort of selected lecture rooms in a university. Two rooms of different sizes and ventilation rates were selected, in which the indoor's air temperature, CO2 content and relative humidity were measured both when occupied and unoccupied. The study revealed that occupancy by students did not directly affect the relative humidity in the lecture rooms, probably due to the dominating influence of the outdoor air. It was found from the study that under high occupancy, the room temperature and CO2 content would be higher than the recommended level and thus affected the comfort level of students and consequently their learning ability during the lecture. © (2013) Trans Tech Publications, Switzerland.