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It is well known that the melting point of metal element drastically change with decreasing the diameter of its particle into nano level, by obeying to the equation as follows, Tnano = Tbulk (1-2s/(DH*R)) Here, Tnano is melting point of nanoparticles. Tbulk is melting point of bulk material, s is surface energy, DH is enthalpy change of melting, and R is radius. Thus, the development of effective and green synthesis method of Fe nanoparticles means the development of new bonding method of Irons at low temperature, since Fe is most basic materials in resent world. Fe nanoparticles were synthesized only in acidic solution by using strong reducing reagent, while it cannot be achieved in basic solution since iron hydroxide, which is easily formed in this condition, cannot be reduced into metals. However, former is not suitable for commercial synthesis method because of its intense reducing process. Thus, the reducing rout of Fe species under basic condition should be developed. Here, until now, we tried to synthesized various metal/alloy nanoparticles, such as Pd20Te7 nanoparticles and uniform Cu-In (CI) alloy nanoparticles, by utilizing the restrict metallic complexes controlling method in an aqueous solution under room temperature. In this method, reduction potential of the metal species can be controlled under the room temperature, consequently metal/alloy nanomaterials with uniform and well crystallized structure can be successfully synthesized. Therefore, in this study, aqueous phase synthesis method of Fe metal nanoparticles were developed. To achieve the homogeneous reaction condition, metal complex species in the aqueous phase were restricted into single species by using calculation. Reduction potential of homogenized metal complex were analyzed by using cyclic voltammetry. Fe nanoparticles were synthesized by using chemical reduction method under ambient conditions using metal chlorides as metal sources and sodium borohydride as a reducing agent. Calculation results indicated that Fe complex can be restricted into one species as the function of pH, complexing reagent species and/also concentration. For example, Fe complex can be restricted into Fe(NTA)2 only, in the case of 8 By using these homogeneous condition, metal Fe nanoparticles were successfully synthesized. Other results, such as melting and/or bonding condition of synthesized materials, will present in our presentation. This work has been supported by the Grant-in-Aid for challenging Exploratory Research (19K22095). [1] H. Takahashi et.,al, Applied Catalysis A: General 392 (2011) 80–85