To develop catalysts with superior stability for isobutane alkylation, La3+ exchanged FAU zeolites with varying framework Si/Al ratios were investigated. Based on the reaction performed in a continuous flow stirred tank reactor, a strong linear relationship between catalyst lifetime and strong Bronsted acid concentration was observed. Catalyst lifetime was speculated to change in an M-shaped pattern with respect to the framework Si/Al ratio, which implies there were at least two extreme Si/Al ratios in terms of catalyst stability. However, their product distribution differed significantly. LaFAU with a high Si/Al ratio led to enhanced acid strength, which resulted in higher cracking, self-alkylation activity, and poor product selectivity. In determining a balance between catalyst stability and product selectivity, a Si/Al ratio of similar to 1.2 was selected as the optimal value for LaFAU zeolites.