Size segregation of granular mixtures is one of the common types of segregation in a rotating drum. This phenomenon occurs in process equipment such as mixers, ball-mills and rotary-kilns. Here, we studied the segregation of bidisperse spherical glass-beads with size ratio ranging from 0.1 to 0.9 in a rotating drum by experiment and DEM modelling. In the experimental part, solidified-bed sampling was applied. For size ratios larger than the transition amount (0.26), the smaller component tended to accumulate in the core region with a maximum core-shell segregation around the size ratio 0.5, whereas in the opposite case (smaller size-ratios), they percolated near the drum wall. At ratios around the transition ratio (0.26) and at size ratios approaching unity, the most uniform concentration of beads was attained based on the relative standard deviation (RSD). (C) 2020 Elsevier B.V. All rights reserved.