We report on the application of a silicon micromachined lamellar grating interferometer in a Fourier Transform Infrared (FTIR) spectrometer for the detection of gases in the mid-infrared (MIR) region. The FTIR spectrometer was equipped with MIR optical fibers for light coupling. Gas measurements in the MIR region were focused on specific gases (CO2, CH4) in order to determine the limit of detection and the selectivity that could be obtained using such a micro-spectrometer. The influence of humidity on the gas response has also been investigated. Using two different spectral regions we were able to detect concentrations of carbon dioxide over a span from 100 ppm to 9000 ppm with a theoretical detection limit evaluated at 10 ppm. The performed gas measurements showed the proof of principle of a miniaturised FTIR gas analyzer based on a micromachined spectrometer.