The sheets of polycarbonate (PC)/polyethylene (PE) in situ microfibrillar composites are successfully prepared directly through multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs) instead of the secondary processing. The morphological development of the PC dispersed phase in PE matrix with increasing the number of LMEs during multistage stretching extrusion investigated by scanning electron microscope shows that core-skin structure of the microfibrillar PC/PE composites during multistage stretching extrusion with 4 LMEs is weakened, and the diameter of the PC microfibrils is relatively more uniform, indicating that the shear field in LMEs greatly affects the morphology of PC dispersed phase in PE matrix. The tensile, crystalline, melting, orientation and rheological behavior of the PC/PE microfibrillar composites are also investigated. The results show that the PC microfibrils are helpful to increase complex viscosity and yield stress of the PE/PC composites. In addition, it is found that the glass transition temperature of PC in PE matrix reduced with increasing the number of LMEs during dynamic rheological testing. It is coincided with the results of DSC analysis of the PC/PE composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40108.