Viscoelastic damper dissipates energy through shear deformation of the viscoelastic material, and this causes temperature rise and softening of the material. Under long duration load, however, significant heat conduction and transfer can occur and control the temperature-rise effects. These and frequency sensitivities are included in the two analysis methods proposed: The first method combines three-dimensional heat transfer analysis and static analysis using a common finite element model of the damper, and estimates damper dynamic properties under long duration load. The second combines one-dimensional heat transfer analysis and viscoelastic constitutive rule using fractional time-derivatives of stress and strain, and it calculates step-by-step the force-deformation time histories of the damper. Good accuracies of both analysis methods are demonstrated by comparing with the results of experiments applying cyclic loading of long duration.