We propose and experimentally demonstrate a plasmonic polarization nano-splitter composed of asymmetric optical slot antenna pairs. Broadband polarization-controlled unidirectional surface plasmon polariton (SPP) launching and splitting are achieved experimentally using an asymmetric optical slot antenna pair array. Both transverse-electric and transverse-magnetic-polarized incident light is coupled to SPPs on the metal surface, but with opposite directions. The measured extinction ratio for the two opposite propagating directions is larger than 5 dB within a bandwidth of 160 nm and reaches up to ∼12 dB at an incident wavelength of 790 nm. This plasmonic polarization nano-splitter, together with the polarization-controlled unidirectional SPP coupler, may have promising applications in the nano-optics and integrated optical circuits.