9 January 2015 Last updated at 08:46 GMT
Adventurers visit Yosemite National Park in the United States to conquer the steep rock face.
Free climbing means Tom and Kevin will use just their hands and feet to climb, rather than pulling themselves up on ropes.
But they will be attached to a safety rope to stop them from falling.
The two climbers will try to free climb the steepest part - the Dawn Face.
Young adventurer Ella has climbed El Capitan and visited Newsround to describe her experience.
Climbers Tom Caldwell and Kevin Jorgeson are hoping to break a world record today by free climbing part of El Capitan.