This paper investigates the influence of fines on the strength properties and deformation characteristics of abraded ballast fouled with two kinds of fines: a fouling made by stone dust of the same parent rock and a clay-based fouling made of kaolinite particles. The results of these tests showed that the fouling containing clay reduces strength owing to a lubricant effect permitting the rearrangement of grains, while the natural fouling has strengthened the sample. The introduction of small rigid particles has induced more homogenized force distribution around the large particles, creating a more stabilized sample.