A novel cubic perovskite MnCu3V4O12 has been synthesized at a high pressure and high temperature of 12 GPa and 1373 K. This compound crystallizes in the A-site-ordered perovskite structure (space group Im (3) over bar) with lattice constant a = 7.26684(10) angstrom at room temperature. The most notable feature of this compound lies in the fact that the Mn2+ ion is surrounded by 12 equidistant oxide ions to form a regular icosahedron; the situation of Mn2+ is unprecedented for the crystal chemistry of an oxide. An anomalously large atomic displacement parameter U-iso = 0.0222(8) angstrom(2) is found for Mn2+ at room temperature, indicating that the thermal oscillation of the small Mn2+ ion in a large icosahedron is fairly active. Magnetic susceptibility and electric resistivity measurements reveal that 3d electrons of Mn2+ ions are mainly localized, while 3d electrons in Cu2+ and V4+ ions are delocalized and contribute to the metallic conduction.