Gary Tasker, the Director of Development and Marketing, said: "Since the tickets first went on sale demand has been stronger than ever before and this confirms that the fans have reacted well to the Final's re-positioning at a later date in the calendar.
"It also follows a developing trend after sell outs at four major fixtures last year and this year's Northern Rail Cup Final. Exciting matches and great family atmospheres are attracting more people to Rugby League".
The RFL has also appealed to Cup Final ticket holders to ensure that they arrive in sufficient time because bag searches and security checks will be undertaken as they enter the Millennium Stadium. Tasker added: "We are taking as many sensible precautions as we can to ensure the safety of people attending this important fixture.
"We want to make as many spectators as possible aware of the situation so that they can allow for the security checks in their travel arrangements".
Millennium Stadium Chief Executive Paul Sergeant said: "We're thrilled to have another sell out at the Millennium Stadium.
"We're certain it'll be a fantastic day out for all the fans but, bearing in mind that it will be a Bank Holiday weekend, can we appeal for everybody to leave plenty of time for their journey to Cardiff."