Obama rolled up his sleeves to spruce up a school with his wife and other volunteers
Barack Obama is due to be officially sworn in for his second term as US president in a small ceremony at the White House.
Although the US Constitution requires the oath of office to be taken by noon on 20 January, as that falls on a Sunday the public inauguration will take place on Monday.
Obama will take his official oath in the White House's Blue Room.
The public ceremony with pomp and circumstance will follow a day later.
Thousands of workers and volunteers have been working to finish construction for Monday's celebration, with white tents, trailers and generators being set up along the Washington Mall's parade route as nearby buildings were adorned with red, white and blue bunting,
For his part, Obama rolled up his sleeves and donned gloves to spend Saturday sprucing up a school with other volunteers, as part of a National Day of Service kicking off the inauguration ceremonies - similar to the way he spent the day before his first presidential inauguration in 2009.
He urged volunteers to honour the memory of civil rights leader Martin Luther King, whose birthday, a national holiday, falls on Monday. This year is the 50th anniversary of Luther King's march on Washington.
President Obama's second term work will be more of a challenge than Saturday's school work, says the BBC's Ben Wright in Washington: Trying to change America's gun laws, reforming immigration and dealing with the country's debt.
In 2009, nearly two million people crammed into Washington to witness President Obama's first inauguration.
Four years on, the mood is unlikely match that excitement, says our correspondent.
But, he adds, the second inauguration of America's first black president is moment many won't want to miss.
Hundreds of thousands of people are expected in Washington for that event - a smaller number than the 1.8m who flocked for the swearing-in of the nation's first black president in 2009.
They will crowd onto the Mall leading to Congress wrapped up against the cold, to see their president take the oath of office on the steps of the flag-draped Capitol and listen to his speech.
The day will include music from Beyonce and Fun, parades, black tie balls and very tight security.