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Sensor setup for the measurement of gas sensing behavior was designed using square glass chamber with gas flow control facility. Polyaniline (PANI) and polyaniline/magnesium chromate (PANI/MgCrO4) composites were synthesized by single step insitu polymerization technique and characterized by Fourier transform infrared spectra (FTIR) & scanning electron micrograph (SEM), which confirms the presence of MgCrO4 in PANI matrix. The variation of resistance with temperature suggests thermally activated exponential behavior. Using the designed gas sensor setup, authors have studied the change in resistance with concentration of liquid petroleum gas (LPG) of polyaniline and polyaniline/magnesium chromate composites. The increase in electrical resistance and hence decrease in conductivity is due to transfer of charge from sensing material to analyte gas and penetration of gas into the polymer, accompanied by swelling of polyaniline and its composites. The time response of sensor chamber shows that, there is a linear increase in concentration of gas inside the chamber with time.