Accurate estimation of resting energy expenditure (REE) in children and adolescents is important to establish estimated energy requirements for the Japanese population. Our objectives were 1) to determine the REE of 6- to 17-y-old Japanese children and adolescents by indirect calorimetry in order to estimate energy expenditure for this group, 2) to compare measured REE with predicted REE to determine the accuracy of predictive equations of REE for Japanese children and adolescents, and 3) to derive new predictive equations for REE for Japanese children and adolescents based on measured REE. REE was measured in 221 Japanese children and adolescents, aged 6 to 17 y old (113 boys and 108 girls) using a ventilated indirect calorimeter. Anthropometric and body composition measurements were also performed. REE expressed as absolute values increased with age in both genders, and there was a significant difference between genders in the 12-17 y age group. REE was strongly correlated with body weight (BW) and fat-free mass (FFM). REE adjusted for BW or FFM decreased with age in both genders, and a gender difference was still observed in the 12-17 y age group after this adjustment. The highest accuracy of prediction was achieved using the Dietary Reference Intake for Japanese (1969) for boys and the Molnar equation for girls. Step-down multiple regression analysis was carried out using either a combination of age, gender, BW, and height, or a combination of age, gender, FFM, and fat mass (FM). The predictive equation accounted for 75% (R2) and 76% of the variance, respectively. In conclusion, absolute REE increased and REE adjusted for BW or FFM decreased with age. The major determinant of REE was FFM, but significant gender differences were observed in the 12-17 y range for both absolute REE and adjusted REE.