Abstract. Several samples of potato flour extrudates were obtained by simple and screw extruder. The effects of process variables (moisture, temperature) were related to the following extrudates features: expansion, density, and shearing stress. The microstructure of the extruded products was examined by mercury porosimeter. Total porosity and changes of the average pore radius were stated in relation to physical properties of the extrudates. Total porosity decreased when the expansion of the products increased. Feed moisture was the principal determinante of physical strength, and affected changes in the number, size and distribution of the pores.