The influence of glass bead content and the loading rate on the mechanical properties of polyacrylonitrile/styrene acrylate (ASA) copolymer was investigated. For this copolymer, tensile yield strength and work to fracture were significantly reduced as the bead content was increased. Tensile yield strength decreased linearly with increasing glass bead content according to the Leinder equation. It was found that the variation of tensile yield strength with log(loading rate) follows that of Eyring’s equation for yielding. The presence of the weldline reduced the tensile yield strength of both unfilled and filled materials. Flexural modulus and flexural strength also varied in a predictable fashion with glass bead concentration. The increase in modulus with glass bead content followed Kerner’s equation. Crack growth resistance values of the unfilled ASA and its composites were measured at three loading rates using the generalized locus method. It was found that the resistance to steady crack propagation, J(R), was a sensitive function of glass bead content and loading rate. Within the range of these experiments, JR decreased with increasing glass bead content and loading rate.