The fire broke out at around 4:30 a.m. in the 2100 block of east Westport Drive. Crews arrived to find flames shooting out of a second story unit. It took firefighters about 40 minutes to put the flames out, said Anaheim police Lt. Bobb Dunn.
The victim, identified as Justin Jewell, 17, of Anaheim, was found deceased inside a bedroom.
The Red Cross is assisting the 20 displaced residents.
A cause for the fire was not immediately known.