The Prince wrote: "As Vice Patron of the Welsh Rugby Union I join with the whole of Wales in wishing you every success in the Rugby World Cup in New Zealand."
He said the squad should take pride from the results of the summer fixtures which took place before the start of the tournament.
Wales captain Sam Warburton said: "We are delighted that the Prince has taken the time to send us such a positive message.
"Many of us have met him and we know he is a genuine supporter who wants the team to do well.
"The squad really values the support we get from all quarters and it certainly adds to the positive feeling we currently have in the camp."