The catalytic cracking of tar derived from biomass gasification was investigated, focusing on the catalyst performance of HZSM-5 (Si/Al = 25) loading with Ni or Ni and MgO, which was pre-calcined and reduced at 500 degrees C. The catalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and temperature-programmed desorption (TPD). The liquid and gaseous products were analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC). The results showed that the catalytic activity of Ni-MgO/HZSM-5 was better than that of Ni/HZSM-5. When the loadings of Ni and MgO (mass %) were 6 and 2 wt %, respectively, tar conversion attained 91.03 wt % and the heating value of gas released reached 7.64 MJ/Nm(3). Ni-MgO/HZSM-5 showed a stronger resistance to carbon deposition (11.69 wt %).