Steady-state friction and wear behaviour of as-cast and T6-treated hypoeutectic Al-Si-Mg-matrix composites reinforced with 19.5 vol.% of Al18B4O33 whiskers dry sliding against 5CrNiMo steel counterface have been investigated as a function of applied load and sliding speed. Owing to the severe interfacial cracking and fracture of whiskers which occurs under higher applied load conditions, the composites exhibited a transition from mild wear to severe wear over the applied load range from 45 to 230 N. By comparison with the as-cast composite, the T6-treated composite, with reduced whisker strength and weak whisker/matrix inter-face, had relatively low wear resistance. Under low applied loads, increasing sliding speed caused deep surface damage, thus indu-cing an increase in wear rate and coefficient of friction. As the sliding speed further increased, the formation of a mainly Al2O3 transfer layer on the worn surface and the strain-hardening of the subsurface layer contributed to decreases in wear rate and coef-ficient of friction of the composites.