Summary: This study investigated the effect of fermentation on the physicochemical properties of β‐glucans in oat sourdough. Sourdoughs were produced from oat using homo‐fermentative lactic acid bacteria, Lactobacillus plantarum 22134. The contents of total β‐glucan and soluble β‐glucan, the molecular weight (MW) of β‐glucan and the viscosity of the extracted β‐glucans were determined at 0, 4, 8, 10 and 12 h of fermentation. The total β‐glucan content decreased from 4.89% to 4.23% after 12 h of fermentation. The soluble β‐glucan concentration increased from 1.89% to 2.18% and then decreased to 1.97% after 8 h of fermentation. The content of β‐glucans with MW > 105 decreased from 0 to 4 h of fermentation, followed by an increase and then a decrease after 8 h. The oat sourdough fermented for 8 h had high viscosity, which could be more beneficial for health and bread texture quality, especially for gluten‐free breads. The oat sourdough fermented for 8 h could retain high viscosity, which may be more beneficial for health. [ABSTRACT FROM AUTHOR]