Maria Gomez Valbuena's appeal was rejected by the court, ThinkSpain reported Tuesday.
Valbuena, 87, was convicted in April for being behind a number of cases of babies taken from their natural mothers, who were told they were stillborn, and sold to couples who supported Spanish General Francisco Franco.
Charges against the nun, also known as Sor Maria, came after Maria Luisa Torres, who was told by nuns at a hospital in Madrid her daughter was stillborn, tracked down her daughter, Pilar, 30.
Thousands of children are believed to have been stolen from their birth parents in similar ways.
Valbuena has denied the charges against her and exercised her right not to testify in court.