Furnace slag aggregate with the grain size of 0–11,2 mm from the processing of the waste from the ArcelorMittal Poland landfill in Pleszów near Kraków – Nowa Huta is the subject of the work. The study aimed at the determination of shear strength and bearing ratio of the aggregate depending on water conditions; linear swelling was also determined at different loadings of the sample. The shear strength was determined in a direct shear apparatus, in a box of 12 × 12 cm cross section, with intermediate frames forming 1.0 cm thick shear zone. The samples were formed at the optimum moisture content and the degree of compaction I_S = 0,97, and then sheared directly after forming and after 3-day water-soaking. Bearing ratio and swelling were determined in a cylinder of a volume of 2.2 dm³. The values of the angle of internal friction and cohesion and bearing ratio were relatively high, indicating a high shear strength and bearing capacity of the tested material. Hydration resulted in lower strength parameters and bearing capacity, although these parameters were still relatively high. The aggregate swelling was relatively small. The obtained results of the research were the basis for evaluating the possibility of using the material in question for road construction purposes.