Laboratory scale open-top lysimeters were used for evaluating methane oxidation capacity of stabilized wastes. The acrylic col-umns (Fig. 1) have a diameter of 0.15 m and a height of 1.0 m. They were filled with stabilized wastes obtained from a solid waste dis-posal site in Thailand which has been in operation for more than 20 years. Atmospheric oxygen can be facilitated into the waste layer through natural diffusion at the top of lysimeters. The solid wastes composed of 52.8% plastic wastes and 47.2% of fine fraction (stabilized organic wastes) and their chemical characteristics are shown in Table 1. Initial packing density of solid wastes was set at 270 kg/m3 and 65% porosity, similar to the bulking density of original wastes placed at the disposal site. The columns were purged at the bottom with synthetic gas containing 60% methane and 40% carbon dioxide at different flow rates of 0.5, 1.0 and 1.5 ml/min, equivalent to actual methane loading rate of 8.32, 26.36 and 51.28 g/m3 d respectively. The synthetic gas was used in this study to avoid any inference from other trace gases on methane oxidation reaction. These loading rates were set based on typical landfill gas emission rates from field measurements at the same solid waste disposal site (Chiemchaisri et al., 2006). Dur-ing the experiment, moisture content of wastes was maintained at