Structural stability and energetics of uranium microclusters, U-n (n = 3-13, 27-137), have been investigated by molecular-dynamics simulations. An empirical model potential energy function has been parameterised for the uranium element by using the dimer interaction potential energy profile of U-2, which is calculated by relativistic density functional method. Stable structures of the microclusters for n = 3-13 have been determined by molecular-dynamics simulation. It has been found that uranium microclusters prefer to form three-dimensional compact structures. Molecular-dynamics simulations have also been performed for spherical uranium clusters with sizes n = 27-137.