While the air quality of public facilities such as daycare centers is managed by law, the management of air quality in residential buildings is not mandatory. For this reason, air quality in an apartments has not been well surveyed. In this study, we investigated the influence of cooking and ventilation on the indoor air quality in an apartment. Continuous measurements were performed using real-time monitoring instruments from June 9 to 17, 2014 in Seoul, Korea. A CO2 meter was used to measure CO2 concentration and temperature. A portable aerosol spectrometer (0.25-32 µm), a nanoparticle aerosol monitor (10-1,000 nm), and an aethalometer (total suspended particulate, black carbon) were also used. During the measurement period, ventilation and cooking activities were observed 8 and 10 times, respectively. In 5 of the observed cases, both activities were done simultaneously. During the ventilation, CO2 concentration and temperature were decreased; however, particle concentrations were increased. When cooking was done, particle concentration was increased in some cases; however, CO2 concentration and temperature were unchanged. Combined cased CO2 concentration and temperature were decreased and particle concentrations were increased. Keywords: Apartment, Cooking, CO2, Indoor air quality, Particle, Ventilation