An investigation was carried out on the effects of red mud ratio and UV annealing treatment on the mechanical, thermal and morphological properties of acrylonitrile butadiene styrene (ABS)/red mud (RM) polymer composites. Red mud, in six different concentrations (0, 10, 20, 30, 40, and 50 wt%), was added to ABS to produce composites. The annealing UV treatment was carried out at 100 °C for two different holding times: 100 and 200 h. The mechanical properties, including the elastic modulus, tensile strengths, strain at tensile strength, Izod impact resistance, hardness, density and melt flow index with and without an annealing UV treatment, and the thermal properties, such as the Vicat softening point, heat deflection temperature and melt-flow index, of the composites were investigated. On the basis of the results, attempts were made to establish a relationship between the RM content, the UV annealing holding time, and the mechanical and thermal properties to obtain the best results. The tensile test results showed that the UV heat treatment and red mud ratio were effective for the elastic modulus, tensile strength, and the strain at tensile strength. A considerable increase in the elastic modulus was found with a 50% RM concentration for a holding time of 200 h. The maximum hardness was obtained with 50% RM with UV annealing for a holding time of 200 h. The increased RM content and UV holding time caused the HDT and Vicat values to increased, whereas the melt-flow index and Izod impact strength showed a sharp decreased as the RM content increased to 10%. The addition of RM to ABS changed the wear rate of the composites significantly as well. The structure of the composites were investigated by scanning electron microscopy and compared to mechanical and thermal properties as a function of RM content and UV annealing time.