Abstract: A stable ε-Fe3N magnetic fluid has been successfully synthesized by the chemical reaction between iron carbonyl (Fe(CO)5) and ammonia gas(NH3).The reaction conditions for forming ε-Fe3N magnetic fluid and the relationship between the gas flux ratio and the phase composition of the magnetic particles were investigated.The particle size of ε-Fe3N depended on the hole size of the porous plate.The saturation magnetization was increased with the increase of reaction time.