Abstract: In order to estimate the flux of ammonia adsorbed by the Liao River and entering into the sea, sorption and desorption characteristics of ammonium nitrogen on sediments with different grain sizes in the Western Liao River were investigated by batch experiments of equilibrium sorption-desorption. The results indicated that sorption and desorption of sediments with different grain sizes conformed to the Freundlich and Langmuir isotherms. The sorption capacities of clay and silt were 3643.82 and 2693.71 mg/kg respectively, which were 8.04 and 5.94 times higher than those of the coarse sand. Furthermore, the sorption state ammonium nitrogen carried by clay and silt from the Western Liao River to the sea was 170.10 and 164.52 per kilogram suspended sediments, respectively, which represented 14.99% of the total ammonium nitrogen absorbed by the sediment. The desorption ratios of clay or silt were low, reaching 30.66% and 42.04% respectively. Clay and silt provided the overlying water with 52.15 and 69.16 mg ammonium nitrogen per kilogram sediments, respectively. Furthermore, the sorption state ammonium nitrogen carried by clay and silt was a vital part of the sediment nitrogen cycling. The humus content in clay or silt was much higher than that in the coarse sand, because there was a micro-hole filling sorption mechanism in the aggregate structure. The higher the clay or silt sediment sorption capacity, the lower the desorption ratio.