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Hydrogen sensitivity of as-deposited multiwalled carbon nanotubes (MWNTs) was investigated. The MWNTs were directly coated between microfabricated gold electrodes by a catalytic chemical vapor deposition at 600degC using methane as the monomer. The MWNTs exhibited a higher response > 50% and faster response than conventional metal oxides-based gas sensors in law temperature range of 150-300degC. Furthermore, the selectivity of MWNT-based sensors for hydrogen was investigated with respective to methane. It was found that the sensor signals were in opposite direction when methane was introduced. These phenomena clearly indicated that the MWNTs had a capability to determine hydrogen selectively from hydrogen and methane mixture. In a practical application, hydrogen always emits to the atmosphere with methane or other hydrocarbons. Therefore, the proposed sensor has a capability to determine hydrogen in a hydrogen and methane (or hydrocarbon) gas mixture. In this paper, experimental results are analyzed in scientific and technological view points.