The fire was reported at Willard Avenue and Douglas Street around 12:15 a.m., Capt. Rob Brown said.
A structure to the rear of a residence was "heavily involved" in flames, Brown said.
The blaze was in close proximity to an apartment building to the left and another residence to the right, according to Brown.
Once the fire was extinguished firefighters entered the structure and located a person declared dead at the scene, he said.
Brown did not know whether the victim was an adult or juvenile. San Jose police and an arson investigator were called the scene, Brown said.
Another person was transported for unknown injuries, a fire dispatcher said.
The fire was under control by 1:47 a.m., the dispatcher said.