Various particle-size fractions of soil aggregates were obtained with the wet-screening method from the soil of a long-term stationary fertilization experiment (since 1984) field of the Changwu State Key Loess Plateau Agro-Ecological Experimental Station of the Chinese Academy of Sciences, Northwest China, for analysis of effect of long term fertilization on soil organic carbon distribution in water-stable aggregates of different particle-size fractions. The experiment had five N treatments (N₀、N₄₅、N₉₀、N₁₃₅、N₁₈₀), which were all the same in P application rate, and four fertilization treatments, that is, CK (unfertilized), NP (nitrogen and phosphorus), M (farmyard manure), and NPM (nitrogen and phosphorus plus farmyard manure). Results show that long-term fertilization significantly affected water-stable aggregates distribution (p<0.05), increasing the content of macro aggregates (>2 mm) and decreasing that of micro aggregates (<0.25 mm). Nitrogen fertilization significantly increased soil organic carbon (SOC) content in the 0.5~0.25 mm and>5mm water-stable aggregates by 44.3%~73.3%, compared to that in Treatment N₀. Moreover, Treatments M and NPM increased SOC content in aggregates of all particle sizes by 40.7%~92.2% over CK, and in the >5 mm aggregates by 66.7% and 92.2%, respectively. Treatments N₀、N₄₅、N₉₀ and CK contributed the most to the soil organic carbon content in the 1~0.5 mm water-stable aggregates, accounting for 13.7%~23.7%. Treatments N₁₃₅、N₁₈₀, NP, M and NPM contributed the most to the SOC content in the>5 mm aggregates, accounting for 17.3%~24.9%. SOC was positively related to the content of the>5 mm and 5~2 mm water-stable aggregates, but negatively related to the content of the<0.25 mm water-stable aggregates.