The baby was born last week in the city of Jerez de la Frontera, said Micaela Navarro, the Andalusia region's social affairs minister.
Navarro told reporters the father of the baby is also a minor, and both the mother and the baby were in good health. Her department declined to give further details, such as the sex of baby.
Spanish newspapers said the mother is of Romanian origin. The daily Diario de Jerez quoted medical staffers (Spanish) who treated the girl as saying they were told by her mother that giving birth at such a young age is common in their country. The mother also told staffers the young girl lives with her boyfriend there.
The paper reported that the girl had a relatively uneventful birth: she did not require a cesarean section or to be admitted to the neonatal intensive care unit.
Medical experts warn that because young girls are still growing themselves, they are at higher risk during pregnancy. Studies have shown that teenage girls are more likely to give birth to premature babies and their infants have a higher chance of dying by age one.