Multi walled-carbon nanotubes (CNT) functionalized with ester was used for detecting methane, CH4 gas at room temperature. Quartz substrate with interdigitated prepatterned gold electrodes was employed as transducers and drop casting method was used to deposit the CNT samples. The electrical properties of the functionalized CNT samples in the presence of CH4 gas were studied and the changes of resistance were recorded using digital multimeter. Concentration of CH4 gas was varied from 0.125 % to 1.0 %. The resistance variation of functionalized CNT increased with the concentration of tested gas. Sensor response of functionalized CNT was improved more than 10 % as compared to pristine CNT. CNT-Ester gives the higher sensitivity due to the presence of ester functional group which act as active site to react with CH4 gas. The fast response of functionalized CNT towards CH4 gas suggested that the functional group enhanced the rate of gas adsorption on sensing layer