The invention provides methods for producing nanoparticles having a CuAu type or Cu₃Au type magnetically hard ordered alloy phase. One method includes a step of reducing, in liquid phase, a base metal and then reducing, in liquid phase, a noble metal. Another method includes a step of reducing, in liquid phase, at first a base metal and a part of a noble metal, and then reducing, in liquid phase, a remainder of the noble metal in liquid phase.