The development of microstructure and mechanical properties was investigated in a heavily cold-rolled and annealed AlCoCrFeNi2.1 high-entropy alloy. The as-cast alloy having a eutectic morphology consisting of alternate bands of ordered L12 and B2 phases was 90% cold-rolled. The deformed microstructure showed profuse shear banding and disordering of the L12, but no transformation of the B2 phase. A duplex microstructure consisting of ultrafine equiaxed grains (∼0.60 μm) of disordered face centered cubic and B2 was observed after annealing at 800°C. The annealed material showed remarkable strength-ductility combination having ultimate tensile strength ∼1.2 GPa and elongation to failure ∼12%. © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.