The structural, magnetic and electronic properties of Co 2 MnGe 0.75 Ga 0.25 have been studied by first-principles calculations. Co 2 MnGe 0.75 Ga 0.25 is found to be nearly half-metallic. The calculated lattice constant and magnetic moments are found to be in good agreement with experiments. Furthermore, we investigate the effect of pressure on the electronic structure and magnetic properties of Co 2 MnGe 0.75 Ga 0.25 . The calculated results show a nearly half-metallic to half-metallic (HM) transition at 12GPa. Then the half-metal to metal transition is observed at 97GPa. The calculations show that pressure mainly affects the minority spin states, leading to a slight reconstruction of the minority spin bands with a shift in the Fermi level driving the above-mentioned transition.