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The influence of carbon addition on performance of a lab-scale, anaerobic-anoxic-anaerobic-anoxic sequencing batch reactor ((AO)2SBR) in biologically removing nitrogen and organic matter from liquid swine manure was investigated in this study. The SBR was operated on 3 cycles per day, with 8 hours per cycle at constant 20oC until it reached steady functional conditions. After that, the SBR was subjected to two loading treatments, one with addition of acetate while the other without. The sludge retention time (SRT) and hydraulic retention time (HRT) were maintained at 21 and 3.3 days for the experiment. The results indicated that with acetate addition, the removals of NH4-N, TKN, COD, BOD, and TP are 100.0, 98.7, 97.4, 100.0, and 98.7%, respectively. While without acetate addition, the corresponding reductions are 100.0, 100.0, 97.7, 100.0, and 97.8%. However, both treatments appeared not effective in removing nitrate and nitrite nitrogen due possibly to insufficient time for denitrification, even when carbon was readily available. The removal of dissolved phosphorus by phosphorus-accumulating organisms reached 87.2% with acetate addition but only 67.9% without. A good reduction in total solids (77.5 and 78.8%), total volatile solids (97.0 and 95.6%), total suspended solids (99.9 and 99.3%), and total volatile suspended solids (99.1 and 98.4%) for both treatments was also observed.