Low holding capacity of sandy soils in Florida usually causes losses of nutrients into surface water. Soil amendment is considered as one of the best management practices. However, the use of organic materials as soil amendment is not well addressed. The objective of this study was to evaluate the effects of organic amendment on N and P leaching in two typical agricultural sandy soils (Spodosol and Alfisol) in South Florida. Organic material was amended at the levels of 0, 1.25, 5, 10 g kg ^-1 soil, chemical fertilizer (CF) was applied to each treatment at the rate of 100 mg kg^-1 N and K, and 50 mg kg^-1 P. An additional control (without fertilizer or amendment) was set for background information. All treatments were triplicated. Seven leachings were conducted in 21 days with a total amount of 1813 mL of deionized water comparable to half year's rainfall in the Indian River area of South Florida. Total NH₄⁺-N in the leachate generally increased with elevated rate of organic amendment likely due to mineralization of organic N, with more NH₄⁺-N being released from Spodosol than Alfisol. Unlike NH₄⁺-N, total NO3^--N in the leachate and in soils after leaching decreased with elevated organic amendment, probably due to microbial incorporation. Higher NO₃^--N concentrations were measured in leachate from the Alfisol than from the Spodosol. Total reactive P in the leachate varied with the rate of organic amendment. Total PO₄^-3-P in the leachate decreased and Olsen P in the soil after leaching increased with elevated organic amendment. These results indicate that application of organic materials can reduce the leaching of NO₃^--N and P from sandy soils and maintain more available nutrients for plant use. This effect appears to be related to both soil physical-chemical properties and the rates of organic amendment.