A compact plasmonic 4-way wavelength splitter with band-stop filters at microwave frequencies is proposed. The splitter is based on specially designed plasmonic structures and band-stop filters. The plasmonic structures are placed on the dielectric substrate and consist of two metal gratings with corrugated grooves in the inner surface, which are suitable for integration with planar circuits. The band-stop filters are constructed by composite-periodic grating struc- tures with different groove depths, which can improve the isolations between different branches. The plasmonic 4-way splitter is investigated numerically based on full-wave simulations at mi- crowave frequencies. Electromagnetic (EM) waves at the designed frequencies are confined and guided along different branches with good isolations.