This paper discusses the effect of sleeper size on the cyclic deformation properties of railway ballast under cyclic loading. A series of full-scale cyclic loading tests were performed using sleepers of different lengths and heights, from which it is discovered that the sleeper support setup is basically a center support for 2.0m-long and supports at both-ends for 2.6m-long, though the transit pattern in the deflection shape of sleeper has some variation depending on sleeper length and height. In addition, differential settlement tends to increase depending upon the sleeper shape, indicating the center support state under cyclic loading.