An experimental study was developed to investigate the role of die design (die diameter and die land length) on extrudate expansion, through the Sectional Expansion Inner and Longitudinal Expansion Index. The extrusion-cooking experiments were mane on a corotating twin-screw extruder; at constant specific mechanical energy and moisture content Derailed consideration is given to die geometry and the driving force of expansion. A four-constant empirical model is proposed to describe the expansion indices. The anisotropy of the expansion phenomena is also discussed.