The present work observed the evolution of microstructure in an Al-4Cu-0.3Mg-0.5Cd (wt. %) alloyaged at 200 °?C. The precipitation sequence in this alloy was found to be dominated by the binary Al-Cualloy classical transformation, ie: GP zones -> 0" -> 0' -> ) Analytical transmission electron microscoperevealed that elemental Cd precipitates formed at later stages of ageing. These precipitates wereassociated with the 6' platelets, both on the rim and the broad facet of the precipitates. Small precipitateswith similar morphology with the Cd precipitates were also observed at the early stages of ageing. Thesesuggest that the Cd precipitates provide sites for 8' to nucleate, resulting in an increased dispersion of 6'.On the other hand these also suggest that Cd nucleates heterogeneouslv at the 0 / a interface.