Using the Silva-Bremner method (1966), this paper studied contents of fixed ammonium and maximum ammonium fixation capacities in typical paddy soils derived from seven different types of parent material in Hunan Province. The results showed: ①the content of fixed ammonium in the soils in the plow layer ranged from 69.2 mg/kg to 457.5 mg/kg, being (304.7±93.7) mg/kg on average, and the percentage of fixed ammonium to total N ranged from 2.6 % to 25.7 %, being 14.0 %±5.1 % on average, which was higher than that in the soils of North Hunan. So ammonium fixation was a main N source in the province. In terms of content of fixed ammonium, the seven types of paddy soils were in the order of newly laky clayey soil > yellow clayey soil > alluvial sandy soil > purple clayey soil > grey clayey soil > reddish yellow clayey soil > granitic sandy soil; ②In soil profiles, content of fixed ammonium varied irregularly with the depth from soil to soil, but the percentage of fixed ammonium to total N in soils increased with the depth and on average, it was 15.1 %±6.6. % in the surface horizon, 25.9 %±11.7 % in the subsurface horizon and 15.1 %±6.6 % in the third horizon; ③The newly laky clayey soil was the highest in maximum ammonium fixation capacity in the cultivated horizon, reaching 658.7 mg/kg, and the granitic sandy soil was the lowest, being only 97.6 mg/kg; ④The content of fixed ammonium in the cultivated horizon was correlated with the content of clay of 0.01~0.001mm at the significant level of P_0.01 (r = 0.698^**, n = 28), but not with the content of organic matter, total N, available N, CEC, slowly available potassium or clay <0.001mm in particle size and the maximum ammonium fixation capacity in the cultivated horizon soils was correlated with the content of fixed ammonium and 0.01~0.001 mm clay at the significant level of P_0.01 with correlation coefficients being 0.841 and 0.659^**, respectively.