Mg-9Al-1Zn (AZ91) magnesium matrix composites reinforced by Ti-6Al-4V (TC4) particles were successfully prepared via powder metallurgical method. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) showed a mountain-like tendency with the increase of the TC4 content. The mechanical properties of AZ91 magnesium matrix composites reached the optimal point with TC4 content of 10 wt.%, realizing YS, UTS, and EL of 335 MPa, 370 MPa, and 6.4%, respectively. The improvement of mechanical properties can be attributed to the effective load transfer from the magnesium matrix to the TC4 particles, dislocations associated with the difference in the coefficient of thermal expansion, good interfacial bonding between the Mg matrix and TC4 particles, and grain refinement strengthening.