"Adriano has been a great servant to the club over the last few years and was a key part in our promotion in 2007," said chairman Stephen Lansdown.
"I'd like to place on record my thanks to Adriano for his service and wish him well for the future."
Basso arrived at Ashton Gate in 2005 from Woking and made 182 appearances for the club, becoming a firm favourite with the fans.
He said in a statement on the club website: "When I came to Bristol City I came to fulfil a purpose, that is; make a difference, do something better, add value to the club, to the players and to the supporters.
"So, I'm very grateful to the manager Gary Johnson and assistant manager Keith Millen who gave me the opportunity to show who I am as a player and as a person bringing the best out of people."
Source: BBC Sport
Source: BBC Sport