"It's been a great ride. Looking forward to 3 great weeks," Armstrong tweeted Monday.
A seven-time winner of cycling's most prestigious race, the 38-year-old Armstrong returned to the Tour last year after a three-year absence and finished third behind Astana teammate Alberto Contador of Spain.
Armstrong started a new team for this year's race. He won the race seven straight times from 1999-2005 before retiring.
The Tour de France starts Saturday in Belgium.