The age hardening and precipitation behaviour of a cast Mg--1.3 rare earth alloy has been investigated. Ageing of solution treated and quenched specimens for 3 h at elevated temperatures resulted in a hardness peak for specimens aged at 250 deg C. TEM showed the sequence of precipitation in the matrix was: supersaturated solid solution - > GP zones - > beta ' (on dislocations) - > beta ; and supersaturated solid solution - > beta (formed on rare earth inclusions). It was found that the combined beta ' and beta precipitate dispersions were responsible for the peak in age hardening