The electrical resistivity p, magnetic susceptibility Χ, electronic specific heat coefficient γ e , the Neel temperature T N and the electronic structure and the magnetocrystalline anisotropy energy (MAE) have been investigated for L1 0 -type MnPt alloy system. This alloy system exhibits the characteristic behaviors of pseudo-gap type antiferromagnets, presenting with the highest T N , the smallest values of ρ, Χ and γ e in the vicinity of the equiatomic composition. The values of p, Χ and γ e increase with deviating from the equiatomic composition. From the linear muffin-tin orbital (LMTO) band calculations, the L1 0 -type MnPt alloy system has a pseudo-gap in the electronic structure and the density of states (DOS) at the Fermi energy (E F ) is lowest at the equiatomic composition in accord with the experimental results. Furthermore, the results of the LMTO band calculations including the spin-orbit interaction make it clear that the direction of the magnetic moment of Mn in the equiatomic composition is parallel to the c-axis, consistent with the reported spin structure determined by neutron diffractions. The magnetocrystalline anisotropy constant K is about 1.39 x 10 6 J m -3 which is larger in magnitude than that of L1 0 -type MnNi equiatomic alloy, though the signs are different.