Lack of data on daily inhalation rate and activity of children has been an issue in health risk assessment of air pollutants. This study aimed to obtain the daily inhalation rate and intensity and frequency of physical activity in relation to the environment in Japanese preschool children. Children aged four–six years (n= 138) in the suburbs of Tokyo participated in this study, which involved three days' continuous monitoring of physical activity using a tri-axial accelerometer and parent's completion of a time/location diary during daily life. The estimated three-day mean daily inhalation rate (body temperature, pressure, saturated with water vapor) was 9.9 ± 1.6 m3/day (0.52 ± 0.09 m3/kg/day). The current daily inhalation rate value of 0.580 m3/kg/day proposed for use in health risk assessment in Japan is confirmed to be valid to calculate central value of inhaled dose of air pollutants in five- to six-year-old children. However, the 95th percentile daily inhalation rate of 0.83 m3/kg/day based on measurement for five-year-old children is recommended to be used to provide an upper bound estimate of exposure that ensure the protection of all five- to six-year-old children from the health risk of air pollutants. Children spent the majority of their time in sedentary and light level of physical activity (LPA) when indoors, while 85% of their time when outdoors was spent in LPA and moderate-to-vigorous physical activity. The results suggest the need to consider variability of minute respiratory ventilation rate according to the environment for more refined short-term health risk assessment.