A clamped cubic spline profile taper of an air-filled substrate integrated waveguide (SIW) transition was optimized to search for the optimal design of taper in this paper. The optimization technique involved a combination of the multi-objective genetic algorithm (MOGA) and full-wave analysis of the waveguide. The data from the return and transmission losses provides a basis for the optimization of the transition tapers design. The simulation results show the efficacy of our proposed strategy, where the optimal taper geometry yields an improvement of the return loss while maintaining its original transmission loss at Ka-band (26–40 GHz) frequencies.