The transformation plenomena of γ phase which is formed by heating the ferritic malleable cast iron above Al transformation temperature, and the effects of heating temperature on the hardness were investigated. The results are summarized as follows; 1. By heating the ferritic malleable cast iron above 740℃ α phase surrounded the graphite particle transformed into γ phase. The volume fraction of γ phase is increased linearly with holding time in α ＋ γ region and rapidly with increasing the heating temperature. 2. When the specimens are heated between 740℃-860℃, the grain boundary of ferrite prevent the growth of γ phase. Therefore the interface of γ and α are obserbed along the former ferrite grainboundary. But above that heating temperature the tendency of preventation is weaken, so the interface between γ and α phase are formed irregularly. 3. Having same volume fraction of γ phase, the hardness of specimen are increased with increasing the heating temperature.