We are introducing for the first time a robust method for the preparation of uranium oxide nanofibers with extraordinary thin diameters. We have studied the preparation of U3O8 and UO2 nanofibers by the electrospinning method from uranyl acetylacetonate in mixed organic solvents. Polyvinylpyrrolidone (PVP) was used as a supporting polymer. Besides studying and optimizing the solution systems, we have also examined the effects of collector material on the properties of the fiber mat. We have found that calcination of electrospun green composite fibers deposited on aluminum foil produces U3O8 nanofibers with the lowest average diameter of 20 +/- 5 nm as their adhesion prevents fiber shrinking. We have also studied calcination of fibers on ashless paper and freestanding composite mats. Reduction of U3O8 fibers in H-2/N-2 atmosphere at various temperatures provided uranium dioxide nanofibers with an average diameter of 90 nm. (C) 2019 Elsevier B.V. All rights reserved.