Interactive effect of composts and soils that have different characteristics on N and P releasing potentials of compost-amended soils were examined through a 19-wk leaching experiment using seven composts and three soils (Inceptisol, Ultisol, and Andisol). Availability of indigenous N soils was revealed as the primary soil factor affecting N releasing potential. Only total N concentration of composts were positively correlated with the amount of N in leachates from compost-amended soils consistently across three soils, suggesting that it can better serve as a predictor of N availability in soils treated with composts than other variables such as mineral N. Mineral N (NH₄⁺+NO₃ ^-) concentration of composts was shown to be a possible proxy for N availability of compost-amended soils (Inceptisol and Andisol) with a relatively low immobilization potential. It was also proven that C/N ratio of compost needs to be considered for prediction of N (particularly NH⁴⁺) availability of compost-amended soils. Ultisol with higher available soil P than Inceptisol and Andisol showed the greatest amount of total P in leachates from the compost-amended soils. In Inceptisol and Ultisol, total P concentration of composts was positively correlated with total P amount in leachates from the compost-amended soils. However such a relationship was not found in Andisol which has a high P sorption capacity, suggesting that total P concentration of composts maybe successfully used in predicting P releasing potential of composts in soils with a low P sorption potential but not for soils with a high P sorption potential. Therefore, it is suggested that initial soil N availability and total N concentration and C/N ratio of compost should be considered to predict N availability of compost-amended soils and initial soil P availability and P sorption capacity, and total P concentration of composts for P availability prediction. (This study was supported by the Technology Development Program for Agriculture and Forestry, Ministry for Food, Agriculture, Forestry and Fisheries, Republic of Korea)