Even though several aspects of two-phase configuration might be very significant for efficient anaerobic digestion ( AD) of dairy manure, its application has very been limited. Two sets of experiments daily-fed continuously mixed acidogenic anaerobic reactors with no recycle were conducted to investigate the optimum conditions on anaerobic acidification of unscreened dairy manure in terms of maximum acidification and VS reduction. Effect of solids and hydraulic retention time (SRT/HRT), organic loading rate (OLR), and pH control on anaerobic acidification in terms of volatile fatty acid (VFA) formation and volatile solids (VS) reduction were investigated. Results indicated that SRT/HRT and OLR of 2 days and 15 g VS/L center dot day, respectively, yielded maximum acidification. The pH control was not effective on the acidification of dairy manure. The degree of acidification increases as HRT decreases, and also higher efficiency was determined in an uncontrolled reactor.