The seven-time Tour champion made the announcement via the social networking site ahead of this Saturday's Grande Boucle start in Rotterdam, where the American enters as one of the favourites.
"And yes, this will be final Tour de France," said Armstrong, later adding the "my" to his statement in a separate Tweet, indicating that he wouldn't be riding the 2011 edition of the year's biggest race.
"It's been a great ride," continued Armstrong. "Looking forward to three great weeks."
It will be the end of Armstrong's second comeback to the sport, his first coming after being diagnosed with cancer in October 1996, after which he returned in 1998 and began his run of seven consecutive victories in the Tour de France of 1999.
In 2005 Armstrong retired, only to announce his comeback in late 2008. In 2009 he rode for the Astana squad - under former US Postal and Discovery Channel manager Johan Bruyneel - in a bid to win an eighth Tour crown.
Having failed to win last year's edition and following a major rift with Astana star Alberto Contador - who won his second Tour de France ahead of the American - Armstrong established Team RadioShack, taking the likes of Bruyneel, Levi Leipheimer and Andreas Klöden with him.
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This trio will be part of the squad helping Armstrong in his attempt at that elusive eighth Tour victory, which gets underway with a prologue in Rotterdam this Saturday.
