President Aurelio De Laurentiis released the news with a tweet which also praised the contributions of sporting director Cristiano Giuntoli and managing director Andrea Chiavelli in persuading Raul Albiol to sign.
The Spain international has been a key player for Napoli since moving to Italy from Real Madrid in July 2013 and extending his stay will be a major fillip for Napoli boss Maurizio Sarri.
The tweet read: “Another hit scored by the trio of De Laurentiis, Chiavelli, Guintoli. Raul Albiol has renewed for another four years until 2020 #ADL.”
Napoli are second in Serie A, a point behind defending champions Juventus after five matches. They play host to fourth-placed Chievo on Saturday.