Gas phase methylation of catechol by methanol over modified gamma-alumina catalysts is studied experimentally. The catalyst composition and the reaction conditions are optimized to attain the highest selectivity towards 3-methylcatechol (C-methylation) or guaiacol (O-methylation and to diminish the catalyst deactivation. The modified gamma-alumina {Li+ 3 % Mg2+ 5 %/gamma-Al2O3} was found to be the best with respect to the 3-methylcatechol formation. At 350 degrees C and at a conversion level of 28% the selectivity of 92% towards 3-methylcatehcol was reached. The deactivation was observed to be lower if compared to pure gamma-alumina. Selectivity towards guaiacol formation increased with surface acidity and reached 89% over phosphated gamma-alumina at 270 degrees C. The catalyst structure was determined with a high confidence factor via "full-profile X-ray analysis". The experimental data relating to activity/selectivity as well as catalyst stability to coke formation were explained from the model found for the catalyst structure.