In a commercial landlord's case for rent due, the defendant waived his right to challenge determination of the merits of the dispute by arbitration. Defendant did not oppose a motion by the plaintiff to compel arbitration, and neither objected to the Superior Court's order compelling the parties to arbitrate, not sought any reconsideration of that order. During arbitration, when the plaintiff could produce only an unsigned copy of the lease, defendant objected to the arbitrator's jurisdiction, but proceeded thereafter to present the defense case to the arbitrator. While defendant objected to the award of more than $ 219,000 by the arbitrator, and moved to vacate the award, he never moved to modify or amend his filings in which he conceded the existence of the lease. Through his conduct, defendant waived the issue of arbitrability. A party participating in arbitration without making a timely objection to submission of the dispute to arbitration, may be found to have waived its right to object to the arbitration. Here defendant also filed an answer and counterclaim with the arbitral body in which he represented that he was a party to an arbitration clause contained in a written lease agreement. Under the applicable Commercial Arbitration Rules of the American Arbitration Association a party must object to the jurisdiction of the arbitrator or to arbitrability of a claim no later than the filing of the answering statement. Defendant's failure to object to the arbitrator's jurisdiction in accordance with the very rules to which he agreed to be bound further constitutes a waiver such a challenge. The Superior Court committed no error in declining to vacate the arbitrator's award, and the December 24, 2015 order is affirmed on the grounds set forth in the present opinion.