Two-stage hydrodenitrogenation (HDN)-hydrodesulfurization (HDS) of heavy gas oil, derived from Athabasca bitumen, has been carried out in a trickle-bed microreactor using a commercial NiMo/Al2O3 catalyst. The operating conditions for the experiments were varied as follows: temperature range of 340-420 degreesC, reactor pressure of 950-1600 psig, liquid hourly space velocity range of 0.5-2.0 h(-1), and hydrogen to heavy gas oil ratio of 600 mL/mL. Variation in the catalyst loading between stages I and II was also studied. Stage I products were stripped off any generated hydrogen sulfide and further hydrotreated in stage II to see the impact of hydrogen sulfide interstage removal on the hydrotreating activities. A comparison of the two-stage results to those of the single-stage results shows an enhancement in the hydrotreating activities. For instance, a 12.6 wt % increase in the conversion of nonbasic nitrogen was observed. The optimum conditions for higher gain in HDN and HDS due to hydrogen sulfide removal were found to be 380 degreesC, 7.6 MPa, and 1:3 (w/w) catalyst loading. A Langmuir-Hinshelwood model developed for the hydrogen sulfide inhibition predicts sufficiently the observed data of the two-stage process.