The impact of continuous amending of alkaline materials on soil organic carbon（C）lability remains unknown. The typical acidic purple paddy of double-cropped rice in eastern Hunan province was selected. A paired field experiment was applied to study the labile organic C fractions and extracellular enzyme activities in topsoil at 0-15 cm depth in response to 5 years continuous singly amending alkaline commercial organic fertilizer，quicklime，and Si-Ca-Mg soil conditioner. Comparing to the CK，the content of coarse particulate organic C（cPOC），fine particulate organic C（fPOC），and light fraction organic C（LFOC）in soil increased by 57%-136%，27%-77% and 51%-60%（P＜0.05），respectively，after continuous amending alkaline materials. The ratios of soil labile organic C fractions to total organic C were increased. The content of Ca-SOC raised by 22% and 34%，respectively，after continuous amending lime and soil conditioner. The enzyme activities of β-glucosidase（βG）and N-acetyl-β-D-glucosaminidase（NAG）in soil were significantly reduced by 20% after continuous amending organic fertilizer. The soil labile organic C fractions contents were significantly correlated with soil organic C and available nutrient contents. Continuous input of alkaline materials in paddy enhanced the soil organic C level and lability，which was beneficial to soil C sequestration. The POC and LFOC fractions in soil were sensitive to the alkaline materials input，which could effectively indicate the early change in paddy soil organic C.