The Spain international has completed his move from Real Madrid to the San Paolo for a fee believed to be in the region of 12 million euros on a four-year deal.
The Spain international has struggled to cement a first-team place during his four years at the Santiago Bernabeu, making just 27 appearances last term.
The 27-year-old has been linked with a move to the Serie A outfit throughout the summer and has now sealed a reported 12 million euro switch to the San Paolo, signing a four-year deal.
"Napoli have officially signed Raul Albiol," the club's official website read. "The 27-year-old Spanish defender arrives from Real Madrid and has signed a contract for four years."
Rafa Benitez has also brought the former Valencia man's old Madrid teammate Jose Callejon to the club this summer and has also signed Santos keeper Rafael among others.
The Neapolitans finished second in Serie A last term, but lost coach Walter Mazzarri to Inter and star forward Edinson Cavani to Paris Saint-Germain this summer.