Medium viscoelasticity contributes to the lateral particle migration and particle segregation under channel flows. It is recently reported that the equilibrium positions of the particles in dilute suspensions are greatly affected in a rectangular microchannel by the relative ratio of the medium viscoelastic and inertial forces (Yang et al., 2011). Here, we summarize the forces which may exert on the particles in concentrated suspensions under the viscoelastic flows including inertial lift force, and the shear-induced migration effect arising from particle-particle interaction. In addition, we report some preliminary results regarding particle segregation in concentrated suspensions (i.e., ${phi}_{bulk}=0.05$, 0.1) under both inertial and inertialess viscoelastic flows in the rectangular microchannel. Similar to our previous results in dilute suspensions (Yang et al., 2011), the particles tend to migrate toward low first normal stress regions, and the particle migration is greatly affected by existence of inertia. We firstly report the formation of multi-layered particle trains along the corners in this work. These results give an insight that the medium viscoelascticity would contribute to the design of particle separation devices in complex suspensional flows (e.g. blood cell separation), and also the understanding of particle dynamics in confined environments under viscoelastic flows.