Thermal ageing studies have been carried out with an alumina microsphere-reinforced 6061 aluminium metal-metrix composite (MMC). A solution treatment temperature of 530-degrees-C for 1.5 h and ageing temperature 175-degrees-C with ageing time ranging between 0 and 12 h have been used. It was observed that the hardness achieves a peak value in about 8 h; the ultimate tensile strength shows an increase with increasing ageing time, and reaches a plateau at about 10 h. On the other hand, elongation to failure and impact properties show a sharp decline at approximately 4 h of ageing time. Also, a limited amount of experiments using 175-degrees-C/8 h ageing after solution treatment at 510, 490, 470 and 430-degrees-C for 1.5 h show that the hardness of the MMC deceases steadily as the solution treatment temperature is decreased.