Abstract: Effects of long-term fertilization on labile organic matter and carbon management index(CMI) in reddish paddy soil were studied in order to assess soil quality．The treatments selected in this study were: CK (no fertilizer application); NK (nitrogen and potassium fertilizer); NPK (nitrogen, phosphorus and potassium fertilizer); NK+PM (NP plus pig manure); NPK+RS (NPK plus rice straw).The results indicated that high labile organic matter was the main part among labile organic matter in reddish paddy soil. There were obvious effects of long-term fertilization on labile organic matter fractionation in reddish paddy soil. After 25 year long term application of no fertilizer (CK)，the labile organic matter in soils and CMI were decreased. Soil total organic matter and labile organic matter content in the treatments with fertilizer applied were higher than those in CK and initial soils, and there was significantly increase in labile organic matter and CMI. The CMI in the NPK+RS treatment was the highest; whereas the lowest in NK treatment. The effects on labile organic matter fractionation of combined application of organic with inorganic fertilizer were more significant than chemical fertilizer. The change ranges of soil labile organic matter content and CMI were larger than that of soil total organic matter，of which change range of CMI was the largest. The correlation between CMI and rice yield was significant (p<0.01). This study showed that CMI was a good index to assess influence of fertilization practice on soil quality.