A GaAs-based quantum cascade laser was used to record the absorption spectrum of product gas from a biomass steam gasification plant. The quantum cascade laser, processed as distributed feedback laser, emitted single mode. Its emission wavelength was tuned from 886.76 to 889.16 cm−1 by sweeping the operation temperature of the laser from 185 to 225 K. The spectrum of the biomass steam gasification gas was compared to the measured spectra of C2H4 and NH3 that agree well with the HITRAN 2000 database. The biomass steam gasification gas was found to contain 2% of C2H4. NH3 could not be detected.