We experimentally demonstrate mode-selective excitation of laser-written dielectric-loaded surface plasmon polariton waveguides. The waveguide structures are fabricated by two-photon polymerization of spin-coatable epoxy-based resist on a metal covered glass slide. The waveguides are excited by illuminating the waveguide ends with a strongly focused Gaussian laser beam with a wavelength of 632.8 nm and adjustable polarization. The guiding properties are investigated in the far field by imaging the leakage radiation of the waveguide modes from the metal–substrate interface. It is observed that different TE and TM waveguide modes can be selectively excited with high precision. Simultaneous excitation of the plasmonic TM00 and TM01 modes leads to mode beating and oscillation of the guided intensity between the two sides of the waveguides. In Y-splitters, this simultaneous excitation of the first two TM modes can be used to control the splitting ratio at the exit ports of the splitter.