Ion exchange and thermal stability of hierarchical Y zeolites obtained by the acid and subsequent base treatments of commercial NaY zeolite were studied. It was found that the resulting hierarchical Y zeolite exhibited lower lanthanum ion exchange efficiency and thermal stability compared to the parent NaY zeolite. The introduction of lanthanum in the hierarchical Y zeolite significantly enhanced its thermal stability due to the advantageous combination of the stabilized effect of lanthanum and the reduced content of residual sodium ions. The latter was of paramount importance because the presence of sodium ions promoted breakdown of the hierarchical Y zeolite framework by dislodging aluminum enriched on the zeolite surface during the base treatment. Notably, the generated mesopores facilitated removal of residual sodium ions during the ammonium ion exchange treatment. Consequently, the hierarchical Y zeolite displayed superior thermal/hydrothermal stability even with a low La loading of 3 w t.%.