Ti-Al and Ti-Si alloys were prepared by RF sputtering in a low-pressure argon atmosphere. The microhardness and thermal stability of these alloys were investigated in relation to the structure of alloys. In Al-Ti system, an amorphous phase and AlTi 3 were formed in the composition range of 35-60at%Ti and 60-80.5at%Ti, respectively. In Al-Si system, an amorphous phase was formed for Si content of 45at% or more. Although the microhardeness of Al-Ti alloys shows a maximum at 50at%Ti, its value for Al-Si alloys rises with increasing Si content. These results suggest that the atomic bonding character is different in both alloys, and the covalent character becomes stronger for Si rich Al-Si alloys.