Abstract: Americium (rare earth) nitrate solution is simulated with solution of neodymium, europium and mixed rare earth nitrate, respectively. Their behavior of conversion in microwave heating process is studied. It is shown from thermal analyses, that the converting temperature from rare earth nitrates into their's oxides must be kept at 700～800 ℃. In the stage of denitration by microwave heating the converting temperature can be kept at 520 ℃ and about 30 % of volatilizable component is resided. The product of post denitration is calcined in an electronic fast heating device, and the residual NO x and H 2O can be fully eliminated. The characteristic of final product, such as loose porous, scraped out easily from the denitration vessel is held. The analysis results from X ray diffraction prove that the chemical structure of the product is the same as rare earth oxide.