Phosphorous mobility in soil environments is largely controlled by P sorption and desorption reactions. This study was designed to evaluate the effects of water treatment residual nanoparticles (nWTRs) at different rates on P mobility in biosolids-amended soils. Sorption and desorption batch experiments were performed on two different soils amended with biosolids at a rate of 3% and 3 rates of nWTRs (0.10, 0.20, and 0.30%). The sorption data showed that nWTRs increased the amount of P sorbed by the biosolids-amended soils with the effect increases as the nWTR application rate increases suggesting that more sorption sites were added on the soil surface as a result of nWTRs addition. The modeling of sorption equilibrium data showed that Langmuir model fit the data much better than Freundlich, Elovich, Kiselev Hill-de Boer, Fowler– Guggenheim, and Temkin models, with relatively higher R2values and smaller standard error of estimates (SE). Whereas, the power function and first order kinetics models provided much better fit for the P adsorption kinetics as evidenced by higher coefficient of determination (R2) and lower SE values. Application of nWTRs with different rates to the clay soil drastically reduced the percentage of desorbed P to 6, 4, and 1% from clay soil and to 12, 7 and 4%  from sandy soil at 0.10, 0.20 and 0.30% application rates, respectively. The lack of similarity between adsorption and desorption due to the hysteresis is likely a result of binding to Al/Fe hydroxides. Fourier transmission infrared (FTIR) results indicate the crucial role of surface hydroxyl groups in P retention onto nWTRs.