Teresa Romero, 44, is no longer infected -- although a second test is required before she can be declared free of Ebola, the result suggests, BBC reported.
She contracted the virus when treating two missionaries who had been repatriated from West Africain in a Madrid hospital earlier this month.
Romero tested positive for the virus Oct 6. The missionaries later died from the disease.
She might have become infected when she removed her protective suit, the report said.
She may have touched her face with her gloves after treating one of the missionaries, a doctor in Madrid said.
Romero has been treated at Carlos III hospital and was reportedly given a human serum containing antibodies from Ebola survivors.
The Ebola outbreak has killed more than 4,500 people across West Africa, according to the World Health Organisation latest report.