The diffusion of the oil mist while cooking affects the entire room, leaving stains on the ceiling and walls. The validity of measuring the color difference of stains was examined by installing Teflon plates in the kitchen and the adjacent space with a view to assessing the oil diffusion. Four houses were designated for the examination. In each house, four Teflon plates (20 ×40 mm) were installed on the ceiling and walls of the kitchen and the space adjacent to it. Then, one plate was removed at an interval of one month to measure the color difference (Δ E ab reading) with chroma meter. Δ E ab reading began to increase from the third month and the color difference was evident at different spots. For example, the reading on the ceiling at the corner of the space adjacent to the kitchen was higher than that on the ceiling of the kitchen itself.