A Gloss defect on high-gloss injection-molded surfaces are difficult to control. This paper proposes a control methodology for a gloss defect. The maximum replication factor (RFmax) is an index representing the effect of the molding conditions on the surface gloss. As RFmax increases, the surface gloss is stabilized due to the maximized replication of the mold surface. The process window of the influencing parameters for obtaining a stable surface gloss is predicted by the range of RFmax. The predicted process window suggests specific molding conditions for controlling the gloss defect. Experiments show that the surface gloss is stabilized, and the gloss defect owing to the fluctuation of the filling conditions is suppressed in the predicted process window for poly(acrylonitrile-co-butadiene-co-styrene) and polycarbonate. The novel methodology can be applied to optimize injection-molding technologies, such as sequence valve gating and rapid heat cycle molding.