Hydrolysis of wheat proteins during sourdough fermentation was determined in the present study. Sourdoughs were characterized with respect to cell counts, pH, TTA, and proteolytic activity as well as the quantity of total proteins and water-soluble proteins. Moreover, composition analysis of total proteins and water-soluble proteins using SDS-PAGE was carried out. Sourdough fermentation using Lactobacillus plantarum showed a decrease in pH and increase in TTA during fermentation. Fermentation resulted in hydrolysis and solubilization of wheat proteins. It demonstrated that protein hydrolysis in sourdough was mainly caused by pH-dependent activation of cereal enzymes according to change in proteolytic activity.