Water and sanitation charity WaterAid will receive the proceeds from the Christmas cards sent by Prime Minister Gordon Brown and his family this year.
A third of the price of the cards, which feature the charity's logo, will be donated to WaterAid.
Sarah Brown, the Prime Minister's wife, said in a statement: "WaterAid is a great charity doing vital work that is widely supported by many people in Britain. I know the availability of basic sanitation and clean water is a fundamental part of keeping people in good health."
A spokeswoman for 10 Downing Street said it was not yet clear how much money would be raised for the charity.