The cyclic deformation behaviour of an aluminium matrix composite reinforced with 16% V-f silicon carbide whiskers was studied. The microstructures were designed so that different precipitates existed in the composite. The results indicated that the SiCw/6061 Al composite demonstrated cyclic hardening, however the cyclic response stresses and the cyclic hardening tendency were different under differing ageing conditions. Lower cyclic response stresses and higher hardening tendencies were found under natural ageing conditions, while higher cyclic response stresses and lower hardening tendencies were obtained under artificial ageing conditions. The higher the cyclic response stresses following artificial ageing, the lower the hardening tendencies that reduced fatigue life. The effects of microstructures on the cyclic deformation behaviour of the composite were examined under the TEM and changes in microstructure caused by the cyclic deformation were observed.