Low Co AB5-type Mm(NiCoMnAl)5Bx (x=0~0.2) hydrogen storage alloys were prepared by casting and rapidly quenching. The microstructures and electrochemical characteristics of the alloys were analyzed and measured. The effects of boron content and rapidly quenched technique on the lattice constants, thermodynamic parameters, microstructures and electrochemical properties of the alloys were investigated in detail. The obtained results show that the lattice constants, cell volume and standard enthalpy increased with the increase of boron content. When quenching rate is in a specifically range, the rapidly quenched treatment could enhance the discharge capacity of the alloys. When quenching rate is more than a certain critical value, The discharge capacity of the as-quenched alloy is less than that of the as-cast alloys. The cycle life of the alloys monotonously increased with the increase of quenching rate.