Sourdough fermentation by lactic acid bacteria and baker's yeast with acidification of dough and producing lactic acid and acetic acid has significant effects on quality characteristics of bread. Application of liquid sourdough in bakery industry has attracted much attention due to higher dough yield, ease of transition and one-step process in order to achieve desired texture and flavor characteristics in final product. In the research, Response surface liquid methodology was used to optimize sourdough fermentation for increased acidification. Fermentation time (5.3-18.7 hrs.), temperature (21.6-38.4oC), and dough yield (249.6-350.4) were considered as independent factors according to central composite design and their effects were studied in liquid sourdoughs fermented with Lactobacillus casei subsp casei, Lactobacillus fermentum and Saccharomyces cerevisiae. Lactic acid and acetic acid contents and total titrable acidity (TTA) were considered as the main responses. The second order polynomial models satisfactory predicted the effects of variables on acidification properties (R2adj> 0.80). Statistical analysis showed that all the responses were significantly (P<0.01) correlated to fermentation time and temperature. Increase in fermentation time and temperature was associated with an increase in lactic acid, acetic acid and TTA and fermentation time was the most affecting factor on acidification. Lactic acid was not affected by dough yield but the lower dough yield caused in high acetic acid content and acidity. Based on response surface and contour plots, the optimum conditions for maximum acidification were: fermentation time (21 hrs.), temperature (38oC) and dough yield (DY: 325).