For polymers with long, complicated, branched chains, it is difficult to measure the real shear viscosity and slip velocity, using the capillary rheometer based on the adsorptiondesorption mechanism. In this study, a double-barrel capillary rheometer was used to investigate the viscosities of four polymers including polypropylene, high-density polyethylene, polystyrene, and polymethylmethacrylate in a microchannel. A general model of polymer viscosity based on the entanglementdisentanglement was presented. The proposed model is important in understanding the mechanism of wall slip. This general model can be transferred to the other different models when changing the parameters. Actually, the entanglementdisentanglement model can also be transformed to the adsorptiondesorption model. Using the model, it was found that the viscosities of polystyrene and polymethylmethacrylate were reduced with decreasing die diameter, and the slip velocities were increased with the increase of shear stress which agrees well with polymer microrheology based on the microscale effect. For polymers with long, complicated, branched chains, the proposed model improves the accuracy of the calculated viscosity and gains the real slip velocity when polymer melt flows through a microchannel. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers