In this study, an elastic-plastic thermal stress analysis is carried out on a thermoplastic composite beam. Temperature is chosen to vary linearly along the sections of the beam. The beam is made of steel fibre thermoplastic matrix composite. It is fixed by two rigid planes at the ends. The solution is performed for 0degrees, 45degrees, 60degrees and 90degrees orientation angles. The orientation angle of 30degrees does not give any plastic yielding, for it melts before plastic yielding. The intensity of the residual stress component of sigma(x) is maximum at the upper and lower surfaces of the beam and is obtained to be the greatest for the orientation angle of 0degrees. The equivalent plastic strain is found to be the greatest for 0degrees and 60degrees orientation angles. Plastic yielding begins on the beam at the highest temperature for 45degrees orientation angle.