The Mo/b (beta zeolite) catalyst was prepared by wet-impregnation and modified with cobalt promoter. The catalytic activity of monometallic Mo/b catalyst in selective hydrocracking of tetralin intomonocyclic aromatic hydrocarbons (MAH) such as benzene, toluene and xylene (BTX) was investigatedin fixed bed reactor and compared its activity with bimetallic CoMo/b catalyst. The catalytic resultsindicates that, incorporation of promoter (Co) not only improved their catalytic activity in hydrocrackingreactions but also showed long term stability as compared with Mo/b. Effect of different SiO2/Al2O3 ratio(25, 75, 150) in beta zeolite was investigated on catalytic activity of CoMo/b. CoMo/b with SiO2/Al2O3 of25, gave highest 62.6% of desired MAH yield at 99.5% conversion of tetralin for more than 140 h ofreaction time. Likely, CoMo/b catalyst was also found to be effective for the conversion of pyrolysis fueloil (PFO) into MAH. Crude PFO was distilled out at 170 8C and total amount of 55 wt.% PFO was receivedafter distillation. In the PFO hydrocracking, it produced 43.3% of MAH product yield at 70% conversion ofPFO, which is significantly higher than the conversion (48%) and MAH yield (34.2%) obtained frommonometallic Mo/b catalysts. CoMo/b catalyst was found to be more stable as well as active for longerreaction time (140 h).