Limited data are available for understanding indoor environmental quality (IEQ) and the related healtheffects in schools in China. This paper reports the air exchange rates (AERs) of 50 rooms in auniversity in Tianjin, China, and explores the relationship between ventilation conditions and symptoms.All of the 50 rooms were visited during June to August, 2006, including 20 dormitories and 5 readingrooms using ceiling fans, 10 old classrooms with split air-conditioners in an old building and 10 newclassrooms with air circulation cooling system in a new building, and 5 conference rooms with splitair-conditioners. Temperature, relative humidity (RH), and CO2 concentrations were continuouslymonitored for 12h in each room, and out of the building simultaneously. Occupants in the rooms, allbeing undergraduates, were investigated by questionnaires regarding time-activity patterns, judgmentabout IAE in campus and comfortlessness possibly relative to bad ventilation. Room characteristics,ventilation methods and numbers of occupants and their activities were also recorded. AERs werederived from CO2 concentration decay curves obtained when rooms were unoccupied. CO2concentration, temperature and RH ranged 615~5346 ppm, 18.9~39C and 30~90%, respectively.Average AERs were 1.2, 1.9, 1.6, 1.1 and 0.7 hr-1 in dormitories, reading rooms, old classrooms, newclassrooms and conference rooms, respectively. In dormitories, factors such as outdoor climateconditions, deficiency of building design, room usage and living habits of students, were considered tobe essential on ventilation and indoor CO2 concentration. More complaints and symptoms were foundin dormitories, classrooms and conference rooms, whose AERs were lowest. CO2 concentrations washighly associated with symptoms such as absence of mind, fidget and headache, regardless of thecomfortable temperature (22~28?) and RH (40~70%) range. In dormitories, AER or CO2concentrations was not a key factor influencing comfort, instead, students judgments on IEQ dependedon RH and temperature.