The rare-earth-based AB5-type Mm(NiMnSiAl)4.3Co0.6−x Fe x (x =0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) hydrogen storage alloys were prepared by casting and rapid quenching. The microstructures of the as-cast and quenched alloys were analysed by XRD, SEM and TEM, and electrochemical cycle stabilities of the alloys were measured. The effects of substituting Co with Fe on microstructures and cycle stabilities of the as-cast and quenched alloys were investigated in detail. The obtained results show that the effects of substituting Co with Fe on the phase structures of the as-cast and quenched alloys are imperceptible, but its effects on cycle stabilities of the alloys are notable. Substituting Co with Fe improves slightly the cycle stabilities of the as-cast alloys, but it can significantly enhance the cycle lives of the as-quenched alloys, which is mainly attributed to the grain refinement of the alloys caused by substituting Co with Fe.