To improve the mechanical properties of AZ91D alloy, squeeze casting process was employed to fabricate AZ91D magnesium matrix composites reinforced with stable icosahedral quasicrystal particles which were introduced as Mg-Zn-Y quasicrystal master alloy. The effects of quasicrystal master alloy content on microstructure and mechanical properties of composites were investigated. The results show that squeeze casting process is an effective method to refine grain size. The composites comprise α-Mg matrix, β-Mg17Al12 phases that disperse on grain boundaries and Mg3Zn6Y quasicrystal particles. A stable interface between the quasicrystal particles and the Mg matrix is observed. The composite exhibits the maximum ultimate tensile strength of 194.3 MPa and the maximum elongation of 9.2% respectively when the mass fraction of quasicrystal master alloy is 5%. The reinforcement mechanism is concluded as fine-grain strengthening and quasicrystal particle strengthening.