Abstract: This paper deals with the effects of cobalt on the mechanical properties of Fe-Cr-Ni-Co base superalloy Refractoloy26.Cobalt is replaced by nickel to produce 0,7,14 and the standard 20 pct cobalt versions of the alloy. Tensile properties at room temperature and elevated tempratures,temperature dependence of Young's modulus and shear modulus, and the creep properties at 565℃ and varied applied stresses are experimentally determined. The results ndicate that lowering cobalt content has a little influence on the tensile properties, but a great influence on the creep rate and the stress rupture life. It is proved that the creep properties of the alloys depend directly on the ivalues of stacking fault energy in matrices. The possilility of lowering cobal content in Refractoloy 26 also has been discussed.