Abstract： Objective To compare measurement of energy expenditure(MEE)by indirect calorimetry (IC)with traditional estimation of energy expenditure(EEE),to provide a basis for energy supplementary for critically ill patients.Methods Using self-controlled study,the energy expenditure of 57 intensive care nnit(ICU)patients was measured by IC.Meanwhile,EEE was also calculated using the following equations:Harris-Benedict(HB),HB×factor,or 104.6 kJ/kg.Body weight were calculated using actual body weight(ABW)or ideal body weight(IBW).If body mass index(BMI)<18.4 kg/m2 it was considered as underweight,and the IBW was selected from the IBW table.The potential adequacy of estimated energy was assayed by ratio of EEE/MEE.Results There was significant difference in MEE by IC and EEE by HB,HB×factor and 104.6 kJ/kg [(6335±1004)kJ,(9125±1795)kJ,(7188±1029)kJ vs.(7753±1439)kJ,P<0.05 or P<0.01].There was significant difference between EEE by HB × factor and 104.6 kJ/kg(P<0.01),and EEE by 104.6 kJ/kg×ABW,and the latter was closer to MEE.Underfeeding would occur in most ICU patients if HB equation was used [100%(4/4)in underweight patients and 73.59%(39/53)in normal weight(BMI 18.5-23.9 kg/m2)].EEE as calculated by 104.6 kJ/kg ×IBW was reasonable in the underweight patients 100%(4/4),but EEE in the patients with normal weight by using HB×factor or 104.6 kJ/kg × ABW resulted in significant underfeeding[39.62%(21/53)and 43.39%(23/53)]or overfeeding[24.53%(13/53)and 13.22%(7/53)].Conclusion EEE derived from the equations was extremely inaccurate and may result in significant underfeeding or overfeeding in individuals.On the basis of this study we would recommend IC for measuring energy expenditure in ICU patients.Otherwise,the equations of 104.6 kJ/kg × IBW in underweight and 104.6 kJ/kg × ABW in normal weight patients may be reasonable.