The female nurse was part of the medical team at the Madrid hospital Carlos III that treated a 69-year-old priest who died of Ebola last month, a Spanish health ministry official said on Monday evening.
The woman checked into a hospital in the Madrid suburb of Alcorcón reporting a high fever and has been put in isolation, the official said.
"Two tests were done and the two were positive," a spokesman for the health department of the regional government of Madrid told news agency AFP.
The woman is believed to be the first person to contract the disease outside Africa.
The nurse had treated missionary Manuel Garcia Viejo, who had been working in Sierra Leone when he contracted the disease. He was flown to Spain, but died in hospital within a few days. He was the second Spanish priest to die from Ebola.
The World Health Organization says Ebola has killed almost 3,500 people in West Africa, with the majority of cases in Liberia, Guinea and Sierra Leone.
nm/rc (Reuters, AP, AFP)