Ramos, whose contract with Paris Saint-Germain expired on June 30, said: "It's a very special day, coming home is always a great happiness, now we have to pass medical tests."
The 37-year-old, who carried the colors of Sevilla in the 2004-2005 season before moving to Real Madrid, where he won the Champions League 4 times, added: "I am happy to return and try to join the team as soon as possible."
According to local newspapers, Ramos preferred to return to Sevilla to get a better offer financially than was made by Ittihad Jeddah, champions of the Saudi league last season.
Sevilla occupies the last place in the Spanish league after 4 stages, but will play the Champions League, where he was drawn in Group B along with Arsenal of England, Eindhoven of the Netherlands and Lens of France.
Sevilla were crowned Europa League champions last season.