Using a Holter electrocardiograph (ECG), we recorded the heart rates of ward nurses by working hours and nursing activity. Energy expenditure was calculated from the heart rate data and nurse work lord was evaluated. The following results were obtained. 1) Average heart rates were 77 (beats/min) for day-shift nurse in surgical ward, 76 for evening-shift nurse in mixed, ward, and 74 for night-shift nurse in mixed ward. 2) The energy expenditures per day were calculated to be 3,474 kcal for day-shift nurse in surgical ward, 3,060 kcal for evening-shift nurse in mixed ward, and 3,238 kcal for night-shift nurse in mixed ward. 3) The energy expenditures during working hours were 2,110 kcal/510 min for day-shift nurse in surgical ward, 1,805 kcal/495 min for evening shift nurse, and 2,014 kcal/570 min for night-shift nurse in mixed ward. 4) The highest energy expenditures of nurse engaged in direct nursing care were 834 kcal (39.5%) for day-shift nurse in surgical ward, 632 kcal (34.9%) for evening-shift nurse in mixed ward, and 790 kcal (39.2%) for night-shift nurse in mixed ward. 5) The longest working hours were 174 min (34.1%) in assisting with medical examinations and treatment by day-shift nurse, 155 min (31.3%) in direct care by evening-shift nurse, and 222 min (39.0%) by night-shift nurse. The results indicate that the energy expenditure calculated from the average heart rate of ward nurses in higher than that of other types of workers. The reason for this difference is discussed in this report. Also, this study showed that the energy expenditure determined by this method does not necessarily increase in proportion to working hours.