If laboratory tests confirm the 64-year-old had Creutzfeldt-Jakob Disease (CJD), the human variant of bovine spongiform encephalopathy (BSE) or mad cow disease, it will be the fourth death from the disease in Spain.
"We are currently carrying out tests at a laboratory in Alcorcon to determine if the disease is Creutzfeldt-Jakob or not," a health ministry spokesman told AFP.
Regional newspaper Diario de Leon said the woman was the mother of the last person to die in Spain from the brain-wasting disease, a 41-year-old man who died in February 2008.
The health ministry and regional authorities could not confirm the parental link between the two.
Spain recorded its first human death from mad cow disease in June 2005 when a 26-year-old woman succumbed to it in Madrid.
More than 200 people around the world are suspected to have died, most of them in Britain, from the human variant of the disease, which was first described in 1996.
Scientists believe the disease was caused by using infected parts of cattle to make feed for other cattle.
Authorities believe eating meat from infected animals can trigger the human variant of the fatal brain-wasting disease.
The 27-member EU, of which Spain is part, has banned high-risk materials such as spinal cord from use in feed and stricter labelling was also introduced.