Labile organic matter (LOM) in red soil under long-term fertilization was measured using the KMnO₄ oxidation method.The results show that LOM and carbon management index (CMI) decreased apparently in red soils in Treatment Zero-fertilizer (CK) or treatments applied chemical fertilizer (CK,N,NP,NK,PK,and NPK) after 10 years of cultivation,with the maximum drop (CK) by 40.5% in LOM and 48.1 in CMI;but increased significantly in the treatments applied with manure or with both manure and chemical fertilizers (M,MNPK,and 1.5MNPK),with the maximum rise (1.5MNPK) by 183% in LOM and 195 in CMI.LOM and CMI in Treatment SNPK decreased after 5 years by 25.2% and 31,respectively;but increased after 10 years by 17.9% and 13,respectively.These suggest that chemical fertilizers mainly increase non-labile organic matter content,while manure mainly improves quality of soil organic matter,and straws are slower in the effect than manure.The contents of three fractions of labile organic matter named as highly labile organic matter (HLOM),mid-labile organic matter (MLOM) and labile organic matter (LOM),respectively,were determined using 33 mmol L^-1,167 mmol L^-1 and 333 mmol L^-1 KMnO₄,respectively.Averagely,HLOM,MLOM and LOM accounted for 5.6%,9.6% and 14.5% of total organic matter,respectively.Significant correlations were found among the three with the coefficient between HLOM and MLOM being 0.478,between HLOM and LOM being 0.592^**,and between MLOM and LOM being 0.716^**.Crop yield was also found closely related to MLOM and LOM,with the correlation coefficient being 0.821^** and 0.602^**,respectively,but the correlation between crop yield and total organic matter was insignificant.At the same time,LOM and CMI showed significant positive correlations with cation exchange capacity (CEC),exchangeable potassium,exchangeable calcium,total base and microelement,etc..However,total organic matter was insignificantly related to those chemical indexes.So,LOM and CMI could more than total organic matter objectively reflect changes in soil fertility and soil quality,and should be used as indices to describe soil quality and assess soil management.