Emissions of greenhouse gases (GHGs) from a full-scale contact oxidation emergency sewage treatment plant (STP) in Japan that was damaged by an earthquake and a tsunami were measured. The open chamber (OC) and closed chamber (CC) methods were used to sample the gases emitted in the aeration tank and the settler, respectively. The dissolved gases were measured using the headspace method, and the major emissions sources in wastewater treatment were identified. The results indicated that the GHG emissions from the wastewater were 58.6 g-CO/m (equivalent per cubic meter of wastewater). The CH emissions showed a strong negative correlation with the dissolved oxygen (DO) content. More than 98% of the GHGs were produced and stripped by the aeration tank. The CO, CH and NO emissions accounted for 73.0% (21,781 mL/m), 17.1% (669 mL/m) and 9.9% (10.9 mL/m), respectively, of all GHG emissions. Approximately 1.06% of the incoming chemical oxygen demand (COD) was emitted as CH, and 0.147% of the removed nitrogen was emitted as NO.