Samples of Ultisols different in erosion degree (slight, medium and severe) were collected in Central China and treated with the drying-wetting sieving method for different fractions of water-stable aggregates, >0.25 mm in particle-size. Carbon contents in different components of fumic acid (humic and fulvic acids) in these aggregates were analyzed for characteristics of humic acid in composition, and effects of amendment of different concentrations (0.06 and 0.6g L^-1) of humic acid in the fractions of aggregates from soils different in erosion degree explored. Results show that with erosion aggravating, the content of humic acids in Ultisols and water stable aggregates decreased. In Ultisols slight and medium in erosion, HA carbon content is higher in water-stable aggregates, >4 and 2~4 mm in particle size than in water-stable aggregates, 1~2, 0.5~1 and 0.25~0.5 mm in particle size. In Ultisols the same in erosion degree, fractions of aggregates did not differ much in FA carbon content, except for soils severe in erosion degree, where the fraction (2~4 mm) differed sharply from the fraction (1~2 mm) in FA carbon content. HA/FA ratios in all the Ultisols different in erosion degree were generally less than 1 and the Ultisols medium in erosion degree were higher than those slight or severe in erosion degree in HA/FA ratio in all fractions. Humic acid composition was significantly positively related to content of water-stable aggregates (>0.25 mm), and the correlation coefficients of HA carbon content were the highest (r=0.85^** ，n=19). After amendment of humic acid at 0.06 or 0.6 g L^-1, the contents of all fractions of aggregates increased in all the soils different in erosion degree, and the extent of the increase was higher in 1~2, 0.5~1 and 0.25~0.5 mm fractions of aggregates than in 2~4 and >4 mm fractions of aggregates.