Investigators said a studio apartment in the 100 block of 119th Street went up in flames around 8:30 a.m. When firefighters put out the blaze, they found the unidentified body of a man in his 50s.
"It's tragic, but especially on a day like today, people are traveling to see family members, Christmas Eve," said LAPD Lt. Jeff Nolte. "It's horrific."
Police could not identify the body, but neighbors said a man known to the community as "Blue" lived in the home.
"A lot of people in the community knew of him and knew of the good deeds of which he did," said Andre Davis of South Los Angeles. "He's the kind of gentleman that would more or less give you the shirt off his back."
Investigators would not say if foul play was suspected. They said the homicide and arson investigation was in its early stages.
Anyone with information was asked to call Los Angeles police at (213) 972-7828.