It was investigated the effect of oat whole grain meal’s and everlasting pea’s shares on the course of the extrusion cooking process and on the chemical change in non-starch polysaccharides (NSP) contained in extrudates. It was stated that the mixture of corn semolina and oat whole grain meal could be a valuable raw material for producing extrudates. Owing to the process parameters assumed (temperature distribution profile of the cylinder: 145/165/120°C; moisture content in the raw material: 13,5%; and a die of 3,5 mm) it was possible to stabilize the extrusion cooking conditions at the 18% of the maximum content of the oat whole grain meal in the mixture being extruded. Owing to the effect of extrusion cooking process on the mixtures, there was a decrease in the content of dietary fibre (TDF) and of its insoluble fraction (IDF) in the extrudates, as well as an increase in the content of soluble fraction of fibre (SDF). The level of the changes stated depended on the composition of a given mixture undergoing extrusion cooking. No significant increase in the content of iron, manganese, and nickel in the extruded products was stated compared with their content in the raw material mixtures.