A new intermetallic compound MgYNi4 with Cl5b(AuBe5)-type Laves phase structure was successfully synthesized by both mechanical milling and casting methods. The structural and hydriding properties of the samples were examined by X-ray diffraction measurement, thermal analysis and hydrogen pressure-composition (p-c) isotherm measurement. The lattice parameter of MgYNi4 was estimated to be a = 0.701 nm, which is ca. 2% smaller than that of YNi2. A plateau (miscibility-gap) pressure was clearly observed in the p-c isotherm during the dehydriding process of the sample synthesized by casting. The maximum hydrogen content is approx. 1.05 mass% (H/M approx. 0.6) under a hydrogen pressure of 4.0 MPa at 313 K, and the enthalpy of hydride formation was calculated to be -35.8 kJ/mol H2. The study in this paper reveals, for the first time, an application potential of MgNi2-based Laves phase structure for practical use as hydrogen storage and transport materials.