The bending fracture strength of a commercial WC-Co alloy finished by abrasive flow machining process was examined by three points bending test, using two kinds of specimens pre-processed by wire-EDM and grinding. It was found that this abrasive flow machining process increased the bending fracture strength of wire-EDM pre-processed specimens by 60% and of grinding pre-processed ones by 10% at maximum, respectively. This big strength increase of wire-EDM pre-processed specimens was ascribed to the facts that the abrasive flow machining process changed the surface tensile residual stress to the compressive one and removed micro cracks existed in surface layer. Further the relative small strength increase in grinding pre-processed specimens was discussed on the basis of improvement in surface roughness and decrease in the amount of surface residual stress of compression side, caused by abrasive flow machining process. Finally it was concluded that the abrasive flow machining process is the effective finishing process for a WC-Co alloy with both effects of increasing the strength and giving the enough surface property.