The tertiary butylation of phenol has been investigated over a series of gallium-modified folded sheet mesoporous materials (Ga-FSM-16) with different Si/Ga ratios (Si/Ga = 80, 50, 20) synthesized by the microwave-hydrothermal (M-H) process and characterized by several spectroscopic techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption, temperature-programmed desorption (TPD) of pyridine and 71Ga MAS-NMR spectroscopy. The catalyst Ga-FSM-16 (20) showed the best performance in the acid-catalyzed tertiary butylation of phenol employing tert-butanol as the alkylation agent. A high phenol conversion of 80.3% is observed for this catalyst at a reaction temperature of 160 °C. However, the 4-tert-butyl phenol (4-TBP) yield amounts to 43.3% and the 2,4-di-tert-butyl phenol (2,4-DTBP) yield is 30.3%. Furthermore, due to the large pore size, which allows a faster diffusion of reactants and products, catalyst deactivation of Ga-FSM-16 (20) was not observed even after reaction for 5 h.