Abstract： Objective To investigate the diagnostic value of volumetric capnography in the assessment of asthmatic exacerbation.Methods Sixty-four patients with asthma exacerbation and 20 normal controls performed spirometry and volumetric capnography recording.The patients with asthma were divided into three sub-groups according to FEV1% pred(A:＞80%,B:40%～80%,C:＜40%).Results FEV1% pred,FEV1/FVC,PEF% pred and MMEF% pred were(98±9)%,(80±6)%,(91 ± 15)% and (73±7)% respectively in the control group,but were(52±20)%,(50±10)%,(49±16)% and(28±16)%respectively in the asthma group,the difference being significant(t=6.93-13.29,all P＜0.01).Compared with the control group,dC2/DV[(19±6)%/L vs(31±8)%/L,t=5.09,P＜0.01]showed a decrease in the asthma group.dC3/DV[(2.9±1.2)%/L vs(1.0±0.4)%/L,t=-6.14,P＜0.01] and SR23[(16.8±10.6)%vs(3.3±1.5)%,t=-6.54,P＜0.01]showed an increase in the asthma group compared to the control group,the difference being significant.Compared with that of the control group,dC2/DV[B:(17±5)%/L,C:(13±4)%/L]showed a decrease(t=-11.82,-16.75,all P＜0.01)and dC3/DV[B:(3.2±0.8)%/L,C:(4.1 ±1.2)%/L]and SR23[B:(17.2 ± 3.5)%,C:(28.3±6.9)%]showed an increase(t=2.16-26.08,all P＜0.01)in asthma sub-groups B and C.For dC3/DV and SR23, the difference was significant between asthma sub-groups(t=0.91-22.18,all P＜0.05).In Pearson correlation analysis,dC2/DV(r=0.69.0.54.0.59,0.54,all P＜0.01)and dC3/DV(r=-0.62.-0.45,-0.69,-0.58,all P＜0.01)and SR23(r=-0.75,-0.52,-0.74,-0.62,all P＜0.01)correlated with FEV1% pred.FEV1/FVC,PEF% pred and MMEF% pred. Conclusion Volumetric capnography is a quantitative method for evaluating the severity of airflow obstruction and it can be performed easily during tidal breathing.