Size-induced particle segregation in rotating drums has been investigated using an Eulerian continuum approach (ECA). The mixing process of a binary mixture were respectively predicted in an unbaffled drum, a drum with a "+" shaped central baffle and a drum with a "-" shaped central baffle. Qualitative comparisons with DEM results showed that ECA works well for describing the mixing process of binary mixtures. A mixing index based on sampling information from the computational grids was developed and used for quantitative analysis. Compared with a base case which uses equal-sized particles, the results showed that ECA can separate the effects of mixing from the effects of segregation. However, the rate of mixing were over-estimated and the improvement effects of "+" shaped baffle and "-" shaped baffle were hard to distinguish quantitatively in the ECA. The drag model was modified for improving the ECA. The final segregation was found independent on the initial particle distribution using ECA. (C) 2020 Elsevier B.V. All rights reserved.