Study on the rare earth exchange performance was carried out with high silica, normal silica and low silica NaY zeolites with framework SiO2/Al2O3 ratios of 5.8, 4.8 and 4.6, respectively. It is found that the silicon content of the starting NaY zeolite is one of the significant factors in determining the ion exchange efficiency. The higher the framework SiO2/Al2O3 ratio is, the less selective to the rare earth ions the zeolite will be. However, the efficiency of the use of rare earth ions are comparable to each other when the concentration of rare earth in the ion exchange solution is less than 6 wt.%, no matter the level of the framework SiO2/Al2O3 ratio of the starting zeolites. Comparison of the hydrothermal stability of the rare earth and ammonium exchanged zeolites (REHY) indicates that the REHY sample prepared from the high silica NaY and with the lowest rare earth loading (2.9 wt.%) exhibits the best hydrothermal stability. The reaction studies indicate that the catalyst containing this REHY zeolite shows much better activity and product selectivity in the catalytic conversion of heavy oil than another REHY zeolite prepared from the normal silica NaY zeolite and having a rare earth loading as high as 6.6 wt.%, which is highly probably due to the superior hydrothermal stability of the former zeolite. It is suggested that the REHY zeolite with a low level of rare earth loading prepared from the high silica NaY can be considered as an alternative catalyst for the catalytic conversion of gas oil. (C) 2011 Elsevier B.V. All rights reserved.