The blaze broke out on the 800 block of G Street around 11 p.m. Sunday.
Authorities said two police officers, who arrived at the scene first, tried to rescue a woman in a wheelchair.
"As I got closer to the door, the heat and the smoke became too intense to enter," said Michael Taylor of the San Bernardino Police Department. "At that point, another supervisor arrived on scene and we attempted to try another entry point...but that's when the building was fully engulfed in flames."
When the fire was knocked down, authorities discovered the woman's body.
The cause of the fire remains under investigation.