In a statement, the actress said Dow died "after enduring a long illness."
She was 79.
"It is with great sadness that my brother John and I announce the passing of our mother Nancy Dow. She was 79 years old and passed peacefully surrounded by family and friends," Aniston's statement read. "We ask that our family’s privacy be respected as we grieve our loss."
Dow, an actress and model, was married twice; first to Jack Melick, with whom she had a son, and then to Aniston's father, John Aniston. They divorced when the actress was a child.
Aniston, 47, opened up a bit about her relationship with her mother last year in an interview with the Hollywood Reporter. Explaining that at one point, Dow "was very critical of me," Aniston admitted that they did not always enjoy the easiest relationship.
But more recently, she added, "We're all fine."