The influences of ageing conditions on the strength of a commercial Aluminium alloy 6063 (AA 6063) were studied. Materials in three pre-ageing conditions: 288 h natural ageing (i.e. ageing at room temperature (RT)); 3 h natural ageing; and 3 h natural ageing plus 5 h ageing at 80 degreesC, were subsequently aged at 165 degreesC, 185 degreesC and 205 degreesC from 0.25 to 64 hours. Tensile tests were performed after ageing. Microstructural study was performed using transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM). The results show that for materials with the same pre-ageing condition, the higher the subsequent ageing temperature, the lower the peak strength and the shorter time it takes to reach peak strength. Specimens exposed to longer natural ageing exhibit higher strength during subsequent artificial ageing than those with shorter natural ageing. The contribution of 3-h natural ageing plus 5 h ageing at 80 degreesC to strength is comparable to that of longer natural ageing. Possible causes for such impacts are discussed.