The capacity of a biogas upgrading system based on the microalgae Chlorella sorokiniana was evaluated. A system composed of a photobioreactor connected to an absorption column was tested. Two continuous systems were operated with real biogas. One with biogas containing 1800–3500 ppmv of H2S, another one without H2S. The tested system provided 98% and 100% removal levels for CO2 and H2S, respectively. Removal of H2S was the result of oxidation to sulfate, as a consequence of the high concentration of dissolved oxygen. Comparison of both systems showed no signs of inhibition due to H2S presence in the biogas. It is concluded then that a microalgae-based biogas upgrading system would not only provide conditions for CO2 removal, but also for H2S oxidation.