The ternary alloy LaMg17Ni was prepared by mechanical alloying (MA) and its thermodynamic and kinetic properties were examined. This composite possesses high hydrogen storage capacity of 5.23 mass% at 553 K. Under 3.0 MPa hydrogen pressure, the alloy can absorb more than 90% of its full hydrogen capacity in less than 1 min at 423 K~573 K. X-ray diffraction and SEM were used to characterize the crystal structure, microstructures, and composition of the composite sample. It was found that the MA sample contained a mixture of La2Mg17, Mg2Ni, LaH2 and La particles. The kinetics of the sample was assisted the by catalytic action of Mg2Ni and La as well as the existence of the multiphase structure formed in the preparation process.