Reducing product quality variability is one of the most important issues for the process industry. As product quality attributes (PQAs) are often measured in a laboratory using off-line sensors, direct feedback control is not feasible unless expensive on-line sensors are used. Inferential control provides a means to the solution of this type of problem without the cost of expensive sensors. This paper reports a successful application of control of product quality attributes in a food cooking extruder. It covers the essential steps in achieving the control objective: (1) identifying the influential variables that can be measured on-line and have significant impact on the product quality attributes; (2) estimating a dynamic model between the influential variables and the PQAs for on-line prediction of product quality; (3) on-line feedback control using the influential variables. Experimental results demonstrate that the designed control system not only maintains the quality of the products but also automatically brings the PQAs to user's specification.