Mixing behavior of binary particles with different densities in a wet fluidized bed has been experimentally investigated in this work. Some important hydrodynamic characteristics during mixing, such as the minimum fluidization velocity, flow pattern, and flotsam particle distribution are measured. The differences between dry and wet particles are systematically compared. It is found that the minimum fluidization velocity U-mf of wet particles is higher than that of dry particles due to the liquid bridge force between particles. U-mf reaches its maximum when the liquid saturation S = 0.1, and then decreases, and does not change much when the liquid saturation in the region of S = 0.2-0.3. Liquid addition can bring two opposite effects on the mixing of a binary mixture of particles with different densities. First, the intensity of bubbling in the wet fluidized bed is lower than that in the dry fluidized bed at the same operation gas velocity U-f, which will weaken the mixing. Secondly, the liquid bridge forces between particles can restrain the density segregation, which is beneficial for mixing. A simple method is developed based on the analysis of forces on flotsam particles to evaluate the effect of liquid bridge force on mixing. A segregation index S-e, defined as S-e = F-lift/F-resis, where F-lift contains the drag force F-d and buoyancy force F-b, and F-resis contains the gravitation force F-g and liquid bridge force F-lb, is used to indicate the segregation potential. The calculated results show that S-e > 1 in the dry fluidized bed and S-e < 1 in the wet fluidized bed, and dry particles are more inclined to segregate than wet particles. (C) 2018 Elsevier B.V. All rights reserved.