The 29-year-old's fresh terms will keep him at the Stadio Artemio Franchi until summer 2019.
Valero arrived at Fiorentina from Villarreal in 2012.
"I am really happy to have extended my contract for a further five years," he told the club's official website. "The Viola club has given me so much and as a return I've given them so much.
"In the past few months I told my agent that I didn't want to hear any other offers as I waited to receive one from Fiorentina. My family is very happy in Florence and for me this is crucial."
Valero scored seven goals in 42 appearances for Fiorentina last season.