The micro parts were fabricated by electroforming process of Fe-Ni alloy. Reaction mechanism of Fe-Ni alloy electrodeposition process was investigated using rotating disk electrode. To clarify the rate determining step, the activation energies of iron and nickel elements were calculated from the Arrhenius plot in the temperature range of 308K~328K. The reaction rate of iron in electrodeposition of Fe-Ni alloy was controlled by chemical reaction at temperature range of 308K~318K, while at range of 318K~328K, it was controlled by mass transport. The reaction rate of nickel was controlled by chemical reaction at 308K~318K and by a mixed mechanism of chemical reaction and mass transfer at 318K~328K. For alloy electroforming of micro gears and a mold for powder injection molding, the mandrels of micro gear (1.7mm in diameter and 600 μm in height) and micro mold (550 μm in diameter and 600 μm in height) were prepared by UV-lithography using SU-8 photoresist. Subsequently, Fe-Ni alloy micro gear mold were electroformed with high hardness (490 Hv) and very good surface roughness (Ra 37.5 nm).