Uniaxial extension, biaxial extension and planar extension tests were conducted to obtain the stressstrain curves of rubber specimens in three state s . The parameters of various hyperelastic models for rubber were obtained by the least square method. The static stiffness in three directions of an automotive p owertrain rubber isolator was calculated utilizing the obtained model parameters and compared with the measured. The static stiffness in three directions of the rubber isolator was calculated by using the constitutive model parameters, whic h were fitted by stressstrain curve in different strain levels. Influences of the Mullin effect and the bulk deformation on static stiffness prediction were in vestigated.