Lamb waves are well suited for the interrogation of thin layers which act as waveguides. This paper investigates an experimental scheme for characterizing thermal fatigue damage in composite laminates using linear and nonlinear features of Lamb waves. Specimens were subjected to artificial thermal fatigue to simulate the effect of temperature variation of in-service aircraft composite structures. The experimental observation of the correlation between the acoustic parameters and thermal fatigue cycles in specimens, verifies that Lamb waves can be used to assess thermal fatigue damage and nonlinear feature of Lamb wave can be used to detect thermal damage in early stage with improved sensitivity over conventional linear features. Velocity and attenuation based ultrasonic studies are carried out for comparison with the nonlinear ultrasonic approach and it is found that nonlinear acoustic parameters are more promising indicators to thermal fatigue damage than linear ones.