Sheet molding compounds (SMC) are alternative materials in manufacturing of structural components, automotive components and electrical resistant parts, due to their high strength, light weight, easy formation and low material cost. However, machining is demanded as a secondary process for achieving the final shape of the part for assembly. During machining of SMC composites, some problems are faced because of the different machining characteristics of polymer matrix and fiber reinforcement. In this study, commercial SMC composite including 25 wt.% polyester, 30 wt.% glass fiber and 45 wt.% calcium carbonate, was milled under different depth of cut, feed and cutting speed. Taguchi experimental design was used to determine the effectiveness of the parameters. After the slots were milled, the roughness of the machined surfaces was investigated and it was found that lower feed, higher depth of cut were more effective than cutting speed in decreasing surface roughness.