This study was undertaken to observe the formation behavior of ferro- magnetic phase in Mn-Al-Cu Alloys. The alloy selected for this investigation was 70% Mn-29% Al-1% Cu. This pre-allyed pig was prepared to the cylinderical castings using an Induction furnace after homogenizing at $1100^{circ}C$ for 2hr, the specimens were cooled by cooling methods. Subwequent isothermal heat treatments were followed at $550^{circ}C$ for various periods of time at predetermined(1-1000min). The formation behavior of ferromagnetic phase was investigated by measurements of magnetic properties of the specimens at each stage of heat treatment, and optical microscopic esamination and X-Ray diffraction analyses were also employed. By this basic experimental results, the conclusions are as follows 1) In order to obtain much amount of ferromagnetic phase, the optimum average cooling rate was about 7.35-$16.4^{circ}C$/sec($1100^{circ}C$-$600^{circ}C$). 2) We verified the decomposition of { au} phase to {eta} -Mn and {gamma} , as the specimens were homogenized at $1100^{circ}C$ for 12hr, then heat-treased at $550^{circ}C$ for 1-1000min. 3) A condition of optimum heat treatments in Mn-Al-Cu permanent mag-netic alloys showed that after homogenizing at $1100^{circ}C$ for 2hr, the speciments were cooled in air or furnace(A) and subsequent heat treatments at $550^{circ}C$ for 1-30min. The maximum magnetic properties were measured as follows: Air cooling; Br=1200(Gause), bHc=100(oe), (BH)max=0.07(MGOe) Furnace cooling(A);Br=950(Gauss), bhe=80(Oe), (BH)max=0.05(MGOe)