The present work involves the examination of the age-hardening response at 200 degreesC of Mg-3 wt% Nd alloys, with systematic additions of Zn, and characterisation of precipitate microstructures in peak-aged samples of the alloys using transmission electron microscopy. It is found that, while ternary additions of 0.5 wt% Zn to Mg-3 wt% Nd alloy lead to little change in the maximum increment in hardness, further additions of Zn up to 1.35 wt% result in an appreciable reduction in the maximum hardness increment. The reduced hardening increment seems to be attributable to the formation of precipitate plates that form on the basal plane of the matrix phase.