The effects of various organic functional groups on electrical responses of multiwalled carbon nanotube sensors for H2S detection in natural gas (about 160 ppm) at different operating temperatures (25-80 degrees C) were investigated. The experimental results showed that the amino groups functionalized carbon nanotube nanosensor displayed good chemical sensitivity (25-30%) at room temperature because of -NH reactive sites on the tubes while MWCNT group had excellent performances at higher temperatures. The mechanistic of optimum conditions for functionalized MWCNT based nanosensors and their characterization are strongly going to be discussed. (C) 2012 Elsevier B. V. All rights reserved.