Zeolite HZSM-5 calcined at different temperatures were studied by Si-29 MAS NMR and EPR methods. It is proposed that over a certain temperature range, dealumination did not necessarily occur simultaneously with framework dehydroxylation and thus framework Lewis acid sites may emerge. A two-step mechanism of dehydroxylation may be present, and it dominates the dehydroxylation and dealumination processes at different temperatures.