Wastewater treatment systems are important anthropogenic sources of CH 4 emission. A full-scale experiment was carried out to monitor the CH 4 emission from anoxic/anaerobic/oxic process (A 2 O) and sequencing batch reactor (SBR) wastewater treatment plants (WWTPs) for one year from May 2011 to April 2012. The main emission unit of the A 2 O process was an oxic tank, accounting for 76.2% of CH 4 emissions; the main emission unit of the SBR process was the feeding and aeration phase, accounting for 99.5% of CH 4 emissions. CH 4 can be produced in the anaerobic condition, such as in the primary settling tank and anaerobic tank of the A 2 O process. While CH 4 can be consumed in anoxic denitrification or the aeration condition, such as in the anoxic tank and oxic tank of the A 2 O process and the feeding and aeration phase of the SBR process. The CH 4 emission flux and the dissolved CH 4 concentration rapidly decreased in the oxic tank of the A 2 O process. These metrics increased during the first half of the phase and then decreased during the latter half of the phase in the feeding and aeration phase of the SBR process. The CH 4 oxidation rate ranged from 32.47% to 89.52% (mean: 67.96%) in the A 2 O process and from 12.65% to 88.31% (mean: 47.62%) in the SBR process. The mean CH 4 emission factors were 0.182 g/ton of wastewater and 24.75 g CH 4 /(person·year) for the A 2 O process, and 0.457 g/ton of wastewater and 36.55 g CH 4 /(person-year) for the SBR process.