In comparison with the energy expenditure determined by a whole-body indirect human calorimeter, which provides 24-h energy expenditure (TEE) with high precision and accuracy, the accuracy of predicting energy expenditure (EE) using an activity diary (AD) method was evaluated. Observed and predicted basal metabolic rate (BMR) as well as literature values for typical physical activities were used for TEE prediction. The effect of the number of recorded items in the activity diary on the accuracy of TEE was also examined. Additionally, predicted EE was divided into sleeping, exercise, and sedentary EE to evaluate the estimation errors in the AD method. Subjects were 20- to 69-y-old Japanese women (n = 20) and men (n= 21). Predicted TEE based on the AD was derived by applying the observed or predicted BMR to literature values for physical activities; i.e., relative metabolic rate (R.M.R.), physical activity ratio (PAR), and metabolic equivalent (MET). The BMR value observed for each subject was obtained by indirect calorimetry using a Douglas bag. The BMR for the subject was also estimated from the predictive equations in the 6th revision of the Recommended Dietary Allowances for the Japanese (1999). The correlations between observed and predicted TEE appeared stronger when using observed BMR than those using predicted BMR. Although the difference of mean values between the predicted and observed TEE was small, the limits of agreement between the predicted and observed TEE were around +/- 400 kcal. Predicted EE, excluding the time periods for exercise and rest laying down when determining BMR, showed similar results to those of TEE. Furthermore, the number of recorded items in the AD was not significantly correlated to the accuracy of the predicted TEE (r = -0.03). These findings indicate that the predicted TEE of the AD using observed or predicted BMR and literature values is favorably comparable to observed TEE using a whole-body human calorimeter on a group basis; however, its use as a proxy measure of TEE or EE on an individual basis may be limited.