The structure and microhardness of amorphous and nanocrystalline Al90Y5Ni5-xCox (x = 2,5; 4 at %) alloys were studied. The effect of replacement of Ni by Co on structural and mechanical properties was investigated. This replacement decreases the number of crystallization stages and increases the difference between their crystallization temperatures. Variation of cooling rate controlled by the rotational whee speed (30 to 55 s-1) causes formation of nano-composite material composed of nanoscale fcc-Al particles embedded in an amorphous matrix. The volume fraction of the nanoscale particle and lattice parameter of Al phase were calculated. Amorphous phase reinforced with Al nano-particles shows increased microhardness in comparison with single phase amorphous material.