The MT system was used to estimate the molding stability of a product produced by an injection molding machine. Initially, dimensional transferability was evaluated by using the injection molding machine to produce a thin-walled S-shaped test piece. The state of the machine when operating was indicated by time-varying process data such as electric power consumed, mold temperature, and internal pressure. The S/N ratio of the transferability was used as a signal factor, and the above process data were used as variables in an equation relating the S/N ratio of the machining capability to the pattern of the process state,by applying the two-sided T method. This made it possible to estimate the S/N ratio of a workpiece from the processing data. The process data items were also diagnosed using an orthogonal array, which showed that hold pressure and mold temperature had large effects.