The effect of cold-rolling and high-temperature aging on precipitation processes in an Al–Er–Zr alloy was investigated by microhardness and resistivity measurements, scanning electron microscopy, (scanning) transmission electron microscopy and X-ray diffraction. Many similarities with the Al–Sc–Zr system have been shown. Based on the obtained results, following decomposition sequence of supersaturated solid solution of the Al–Er–Zr-based alloy has been proposed: Er-rich clusters → Al₃Er phase → layer rich in Zr (Al₃(Er,Zr) phase). Cold-rolling enhances the precipitation of Al₃Er particles and accelerates the process identified as formation of the Zr-rich shell around the Er-rich core of Al₃(Er,Zr) precipitates. The effect of precipitation strengthening is negligible compared to the effect of work hardening as the supersaturation of Er in the Al matrix was probably considerably lowered by formation of Er-rich primary precipitates observed in the as-prepared state of the alloys studied. The core–shell structure of the Al₃(Er,Zr) particles formed after 2 and 4 h of aging at 600 °C was confirmed by Z contrast imaging and X-ray energy dispersive spectroscopy. The coherency strain-field around the precipitates is retained even after 4 h of aging at 600 °C. The Er/Zr atomic ratio of the precipitates was estimated based on their lattice constant.