Nonlinear ultrasonic technique using Lamb wave propagation has been used to evaluate creep damage in modified 9Cr-1Mo steel. First, precipitation study was done in this steel using nonlinear Lamb wave to predict the optimum heat treatment condition followed by creep damage assessment. It was seen that nonlinear ultrasonic parameter is highly sensitive to dislocation evolution in the material. Finally, nonlinear ultrasonic using Lamb wave mixing was employed to determine the location of maximum deformation during creep prior to its failure. Nonlinear Lamb wave mixing was implemented to remove nonlinearities from extraneous sources other than material nonlinearities from the received signal.