A cinnamon soil and a lime concretion black soil from Huang-Hai-Hai Plain of China and a Palouse silty loan from eastern part of Washington state of U.S.A. were mixed with wheat streiw (¹⁵N labelled and unlabelled) and nitrogen fertilizer (¹⁵N labelled and unlabelled) in different. rotes and incubuted under 20℃ and 30℃ for 7 weeks to investi;ate the transformation of fertilizer-N and straw-N. More than 70% even all of the mineral N was immobilized in the soils incubated only with straw or low rate of N fertilizer under 200C or 300C after 1 week; and immobilization was dominant in the soils during the imubation from 2nd to the week. While Iess N immobilized in soils ineubated with lihlmr rate of N fertilizer after 1 week;and part of the immobilized N was mineralized in the soils incubated under 30℃ during the perind from 2nd to 7th week. It seemes that the immobilization rate of N in the soils decreased with the increase of fertilizer-N added. At the end of incubation 10-50% of fertilizer-N appeared as miniral-N in the soils with higher rates of N fertilizer. About 50-60% of the fertilizer-N and similar range of straw-N appeared as HCl hydrolpzable N. The immobilization rate decreased with the inerease of organiu matter and total nitrogen contens of the soils and the raising of incubation temperature.