Cooking characteristics of some rice varieties were compared with these of corn before and after extrusion. Gelatinization temperature, swelling power, solubility and amylographic behaviour on native state and the cooking degree attained in the extrusion process were determined. Differential scanning calorimetry was also performed. Results indicate that corn has a higher resistance to swell than rice varieties but a higher solubility than rice varieties with the same amylose content. The gelatinization enthalpy is also higher. The higher the amylose content, the falling of the amylographic consistency during the cooking period (observed with rice samples) the less. Consistency at the end of the cooking step and retrogradation are directly related to the amylose content. All samples were significantly affected by the extrusion variables ( screw speed and die diameter) particularly at 15% moisture content. The degree of cooking increases as die diameter and amylose content decrease. The effect of rpm depends on moisture level, being directly related at 15% and inversely at 30%. The thermograms of extruded samples indicate that at 150ºC extrusion temperature a complete melting of crystallites is not achieved, transitions are displaced to higher temperatures and a lipid complex formation is observed during extrusion, which seems to be higher for 15% extruded samples.