Abstract: The segregation of equal volumes of 2-mm and 4-mm particles inside a 14-cm-diameter spherical tumbler is numerically investigated using the Discrete Element Method (DEM). Two types of segregation take place. Initially, radial segregation appears, and then axial segregation occurs. The radial segregation occurs quickly due to percolation, with large particles moving towards the outer layer and forming a shell, while smaller particles remaining in the center and forming a core. Axial segregation is a slow process in which particles segregate into two different patterns and both with three bands. Smaller particles are at the equator and larger particles at two poles (Large–Small–Large, LSL), or vice versa (Small–Large–Small, SLS), depending upon the particles filling level inside the tumbler and/or the rotation speed of the tumbler. The total tangential force between the tumbler wall and the granular particles decreases rapidly as radial segregation occurs and then becomes almost constant as axial segregation occurs. The circulation frequency of the particles is analyzed, and the results show that the average circulation frequency of the smaller particles along the rotation axis is higher than the circulation frequency of the larger particles. Also, the distribution of the average circulation frequency is uneven. The simulations match up well with existing experimental and simulation results. The results are of common interest in applications like process engineering, where polydispersed granular materials are ubiquitous, and drums and tumblers are universally applied.