Abstract: The paper describes the microscopic appearance of UO_2, U_3O_8, ADU and AUC powders used for the production of sintered UO_2 slug of nuclear fuel component of PWR. The characteristic analysis of the microscopic appearance observed by scanning electron microscope shows that the quality and finished product rate of sintered UO_2 depend on the appearance characteristic of the active UO_2 powder, such as grade size and its distribution, spherulitized extent, surface condition and heap model etc.. The addition of U_3O_8 to the UO_2 powder improves significantly the quality and the finished product rate. The mechanism of this effect is discussed on the basis of the microscopic appearance characteristic for two kinds of powder.