Mg-rare earth alloys have improved yield strength and creep resistance compared to commercial alloys such as AZ91, AM60 or AS21. The influence of Zn additions in Mg–Nd alloys on intermetallic phases and the resulting changes in the macroscopic mechanical behaviour of the materials are not yet fully understood. The aim of this work is to identify the effect of Zn additions on the nature of the intermetallic phases and on the mechanical properties in a Mg–4Nd (wt%) alloy. The addition of 8 wt% Zn to a base Mg–4Nd wt% alloy marginally improved the tensile and compression properties at room temperature or at 200 °C with the exception of the 0.2% proof stress of Mg–4Nd–8Zn alloys when tensile- or compression-tested at 200 °C. Two intermetallic phases, a quasi-binary Mg₃(Zn, Nd) and ternary Mg₅₀Nd₈Zn₄₂, have been identified by the means of electron microscopy and synchrotron diffraction. These results indicate that there are some discrepancies in the current thermodynamic calculations, suggesting an update to the databases may be required.