The objective of this research was to evaluate the chemical composition of wheat-oat and wheat-barley breads produced with oat and barley sourdoughs, respectively, and fermented by a starter culture manufactured by a Lesaffre Bio-Corporation in Łódź, Poland. Sourdoughs were made of oat bran or whole-grain barley flour; their amounts were, respectively, 30, 40, and 50 % of the total weight of flour, and of the ‘LV2’ starter (Saccharomyces chevalieri, Lactobacillus brevis). The oat or barley sourdoughs replaced the wheat flour in the mass dough prepared. The bread containing 30-50 % of the oat sourdoughs fermented by the ‘LV2’ starter had a lower volume and acidity, but a higher moisture than the bread containing 30, 40 and 50 % of barley sourdoughs. Along with the increase in the percentage content of oat or barley sourdoughs in the dough mass, the volume of bread loaves became apparently reduced, but the moisture and acidity of the crumb increased. The bread with 30 % of sourdoughs was characterized by a higher sensory quality (9.6 scores) than the other samples. However, the wheat-oat bread was ranked lower than the wheat-barley bread. The bread with 30-50 % of oat sourdoughs contained more mineral components, proteins, lipids, and total dietary fibre, including the soluble dietary fibre; β-glucans, lignin and cellulose fractions; this bread showed a lower level of hemicellulose fraction if compared with the wheat-barley bread.