Mineral filler-reinforced polymer is an important family of polymers designed to achieve high mechanical impact strength. The state of mineral filler dispersion in a polymer matrix strongly affects the mechanical properties of the product and is an important information for the extrusion-based fabrication process. In this work, a measurement system consists of two ultrasonic sensors, three pressure sensors, a thermocouple, and an amperometer of the extruder motor drive were used to monitor the extrusion of a calcium carbonate powder-filled polypropylene system. Three principal components, most correlated to the state of filler dispersion, were extracted from the data set collected by the multiple sensors and fed as inputs to an artificial neural network model designed to determine the dispersion state of the filler. By using this approach, one is able to achieve an accuracy of better than 0.05 on the dispersion index. This work has demonstrated the feasibility of combining our multi-sensor monitoring system with prinicipal component analysis and artificial neural networks for on-line determination of mineral-filled dispersion in polymers.