We measured indoor, outdoor, and personal exposure concentrations of ozone (O3) at 54 households in Gwangyang from June to September, 2009. The results are as follows. The concentration of ozone in outdoor, 16.53±5.72ppb, was observed two times higher than the concentration of ozone in indoor, 8.22±4.60ppb. The similar arithmetic average ozone were obtained in exposed and controlled areas, 15.16±1.45ppb and 15.25±1.94ppb, respectively. The ozone concentration of an individual smoker was 24.89±7.11ppb, which was higher than that of a non-smoker, 21.01±11.79ppb. The indoor occupant density elevated ozone concentrations. The relatively low concentration of ozone was observed in a house with air conditioner (8.59±4.04ppb) than a house without the unit(10.07±6.43ppb). Keywords : Ozone, Personal exposure, Indoor and outdoor, Case, Control