Abstract: The partial isothermal sections of phase diagram at 750℃ and 900℃ in FeNiCr-W-Mo system have been determined by X-ray and TEM methods. Experimental results show, that when the content of Mo% is higher than 1.5% and 1.0% the μ phase can be formed at 750℃ and 900℃ respectively. When the content of tungsten is higher than 7% the μ and Laves phase can be formed at 900℃ in the chemical composition regime of tested alloys, however the Laves phase can not be formed at 750℃ regardless of the total amount of tungsten and molybdenum. In addition, experimental results have also proved that the traditional electron vacanr number N_v=2.30 for μ phase formation can not be vised in the investigated system.