Fr Miguel Pajares was working as a missionary in Liberia when he became ill.
Nearly 900 people have died from the virus which is sweeping across Africa and has no known cure or vaccine.
Two American missionaries are also seriously ill with Ebola.
Dr Kent Bradley and Nancy Writebol have been flown home to the States for treatment.
Fr Pajares, 75, is the first Spaniard to be diagnosed with the virus and government officials say they're working on brining him home for treatment.
He works for the charity Juan Ciudad and the Hospital Order of San Juan de Dios.
Meanwhile, Christian Aid has said it was scaling up its response to the Ebola outbreak in Sierra Leone.
The charity claims it will target 3.8 million people across the country with potentially life-saving advice on how to avoid contracting the deadly disease.
On Tuesday, British Airways announced it was suspending flights to Liberia and Sierra Leone until the end of August because of the Ebola outbreak.