A study was conducted on the application of oat whole-meal (5, 10, 15%) as a modifier of the structure of corn-oat extrudates. Material for comparison, constituting a point of reference, was oat bran. Additional structure modifiers applied were whole powdered milk, at the rate of 1%, and everlasting pea whole-meal in the amount of 10%. Results showed that oat whole-meal can be successfully applied as a modifier of the structure of extrudates, replacing in this respect the notably more expensive oat bran. The extrudates produced were characterized by microstructure very similar to that of extrudates with a content of oat bran. The extrudates had the characteristic ‘honeycomb’ pore structure. Over the whole range of process parameters applied, total liquefaction of raw material was observed, even at 15% content of oat whole-meal in the blends. Change in the moisture content of the material blends and in the process temperature had a notable effect on the microstructure of the products, causing changes in the thickness of walls of air pockets and in their dimensions, among other things. No deterioration of extrudate microstructure was observed following the application of the additional modifiers – whole powdered milk and everlasting pea whole-meal.