Maria da Gloria Gaspar was attacked by about nine of the 15 dogs in her house, police said. Six others, no more than two weeks old, were not believed to have participated in the attack.
It was not immediately clear why the dogs, mostly mongrels, attacked Gaspar, who was alone in the house where she lived with her daughter and two grandchildren.
Neighbors who heard the loud barking and Gaspar's cries for help called the fire department. Firefighters broke into the house in Rio's upscale Laranjeiras district and removed her alive.
Gaspar died later at the hospital from severe blood loss and cardiac arrest.
Police said the dogs had ripped much of the skin from Gaspar's body and that blood was all over the apartment. The dogs, stained with blood, were taken to a city kennel.
Neighbors told local media that the victim mistreated and kicked the dogs, who belonged to her daughter. They also said the dogs often appeared to be unfed and barked much of the day and night.
In an unrelated incident, two pit bulls attacked a 30-year-old woman on Rio's west side, badly biting her face, arms, legs, stomach and breast, police said. The woman was hospitalized and could partially lose her vision.
Following the attack, about 50 enraged neighbors beat the dogs to death and nearly lynched the dogs' owner before police saved him. He was charged with committing serious bodily injury and could be sentenced to up two years in prison.
