Response surface methodology was used to analyze the effect of screw speed (220-340 rpm), feed moisture (11.0-15.0%, wet basis) and feed rate (22.0-26.0 kg/h, wet basis) on the physical properties (i.e., bulk density, expansion, porosity) of a nutritionally balanced extruded snack food. Regression equations describing the effect of each variable on the responses were obtained. Responses were most affected by changes in screw speed followed by feed moisture and feed rate (P<0.05). Expansion and porosity increased with screw speed and feed moisture whereas the opposite was observed for bulk density. Radial expansion was found to be a better index to measure the extent of expansion than the axial and overall expansions, indicated by a higher correlation coefficient.