Isothermal compression of the GH4169 nickel based superalloy was carried out at a Thermecmaster-Z simulator at deformation temperatures of 930-1050uC at intervals of 20uC, strain rate of 0 . 1-50 . 0 s 21 and maximum height reduction of 60 . 0%. The deformation behaviour of the GH4169 superalloy in isothermal compression was characterised based on the stress-strain behaviour analysis. Constitutive equations described the flow stress as a function of strain rate, strain and deformation temperature were proposed for the isothermal compression of the GH4169 superalloy and a close agreement between the calculated and experimental stress-strain curves is achieved.