In a process for producing xylene by transalkylation of a C9+ aromatic hydrocarbon feedstock, the feedstock, at least one C6-C7 aromatic hydrocarbon and hydrogen are supplied to at least one reaction zone containing at least first and second catalyst beds located such that the feedstock and hydrogen contact the first bed before contacting the second bed. The first catalyst bed comprises a first catalyst composition comprising a molecular sieve having a Constraint Index in the range of about 3 to about 12 and at least one metal or compound thereof of Groups 6-10 of the Periodic Table of the Elements, and the second catalyst bed comprises a second catalyst composition comprising a molecular sieve having a Constraint Index less than 3. The at least one reaction zone is operated under a first set of conditions effective to (i) dealkylate aromatic hydrocarbons in the feedstock containing C2+ alkyl groups and to saturate C2+ olefins formed in the first catalyst bed and (ii) transalkylate C9+ aromatic hydrocarbons with said C6-C7 aromatic hydrocarbon to produce xylene in the second catalyst bed. Periodically the supply of the feedstock and said at least one C6-C7 aromatic hydrocarbon, but not the hydrogen, to said at least one reaction zone is interrupted and the first and second catalyst compositions are contacted with the hydrogen under a second set of conditions effective to enhance the activity of the first and second catalyst compositions.