Abstract: Fluidization of binary particle mixtures occurs in a wide range of applications, such as solid fuel combustion, polymerization and segregation. Currently, the available macro-scale fluidization models, e.g. the two-fluid model (TFM), rely on solid-solid (S-S) drag expressions. Previous studies in binary fluidization have assumed that particles are simplified versions of kinetic theory to derive expressions for the drag coefficient. Theoretically, the expression is only valid for dilute regimes. To overcome this, we proposed an S-S drag model for dense flow regimes based on a modified Stokes law. This S-S drag model was validated with experimental data of bubbling fluidized beds with density and size differences. Simulation results were compared with those obtained using the previous models to illustrate the differences. This new S-S drag model predicts more reasonable results for density and size segregations compared to previous studies.