A spokesman for the race said the sister of the Duchess of Cambridge and their brother James are doing the Vasaloppet race to raise money for the child hunger charity Magic Breakfast.
First held in 1922, the Vasaloppet is one of the world's oldest cross-country races. It stretches from the village of Salen near the Norwegian border to the central town of Mora.
The race is based on Gustav Vasa's attempt to gather peasants for a revolt against occupying Danes in 1522. He fled after getting no support, but the people changed their minds and sent their best skiers to bring him back.
The Associated Press contributed to this report.