Thermal degradation behavior of mixtures of rice bran (RB) and high density polyethylene (HDPE) was investigated by thermo-gravimetric analyses (TGA) under dynamic conditions in nitrogen atmosphere and was compared with that of individual materials. Experiments were carried out in the range of ambient temperature to 900 ℃ at two heating rates (5 and 20 ℃ per minute). Kinetic analysis indicated that activation energy for pyrolysis of RB, HDPE and those for RB-HDPE mixtures varied with rate of heating as well as with the three temperature ranges. This variation has been explained on the materials’ decomposition behavior. Maximum difference between experimental and theoretical mass loss (Δm) was 26% at 475 ℃ and 34% at 489 ℃ at the heating rates of 5 and 20 ℃ per minute, respectively. These maxima indicate stronger interactions at corresponding temperature between RB and HDPE during copyrolysis. Reduction in activation energy for pyrolysis, lower temperatures at which rate of decomposition is highest, and negligible quantity of the residue suggest a synergism between thermal degradation of RB and HDPE.