In this study, we theoretically investigate the optimized sleeper spacing which can suppress resonances. We introduced a minimization problem in which the objective function is given by the wave transmittance and the design variable is defined by sleeper distribution. In the analysis the rail is modeled by a Timoshenko beam and the sleeper is represented by a mass. The infinite track analysis is realized by attaching the transmitting boundaries at both ends of the finite optimization region. Through numerical analyses the sleeper spacing effective in reduction of the transmittance is defined. Furthermore, the feasibility of the proposed method is validated through response analyses for a harmonic load.