A novel polarization rotator (PR) based on mode coupling in plasmonic waveguides is demonstrated by simulation. A silicon waveguide with asymmetric claddings of silicon oxide and metal is applied to induce a hybridization of the polarization modes. Operating at the telecommunication wavelength of 1.55 μm, polarization conversion efficiency of 99.7% can be achieved in a device at a length of 9.7 μm with an insertion loss of 2.2 dB. This PR can be easily fabricated by oblique deposition of the claddings after etching the silicon waveguide without precise alignment for two-step lithography as required in a previous design.