Microstructural and mechanical properties of the extruded a-13 duplex phase brass alloy with elemental Mg powder were investigated in this present study. Pre-mixed Cu-40Zn powder with 1.0 mass% pure Mg powder (Cu-40Zn+1.0Mg) were mixed and consolidated by spark plasma sintering (SPS). SPSed Cu-40Zn+1.0Mg consisted of a+0 duplex phase containing CuMgZn intermetallic compounds (IMCs) with a mean particle size of 10 gm in diameter. The IMCs were completely solid soluble in the a+P duplex phase by the heat-treatment at 973 K for 15 min. The SPSed Cu-40Zn+1.0Mg was pre-heated at 973 K for 15 min and immediately extruded. The extruded specimen had fine a+p duplex phase, containing fine precipitates of the above CuMgZn IMCs with 1.0 ium in diameter, instead of the coarse CuMgZn IMCs. The a+13 phase grain size was an average value of 1.99 gm acquired by electron back-scattered diffraction analysis. The tensile properties of the extruded specimens were an average value of yield strength: 328 MPa, ultimate tensile strength: 553 MPa, and 25 % elongation. The extruded Cu-40Zn+1.0Mg revealed the high strength properties. The high strengthening mechanism of the wrought brass alloy was mainly due to the grain refinement of a and P phases because of the pining effect by the fine CuMgZn precipitates in the boundaries of each phase.