Prop Asotasi, 27, joined the Rabbitohs from Canterbury in 2007 and played his 150th match in the NRL against Sydney last Monday.
He has signed for an extra two years on top of his original five-year deal signed back in 2006 amidst interest from Super League clubs.
Rabbitohs CEO Shane Richardson said: “Roy Asotasi has been one of the driving forces of our side over the past three years and we’re delighted to have him commit to the Club until the end of 2013.
“Roy is one of the best, if not the number one, prop forward in the game.
“He carries us forward each and every week and is one of the leaders of not only the team, but the Club as well.
“The other players look up to him, they follow his example, and he is very important to the future success of South
Asotasi has missed just one game in his three years at the club, although he missed last year’s end of season World Cup with a pectoral injury.
He said: “I’m really happy to have my contract sorted out and I’m glad that I will be playing for the Rabbitohs for at least the next four seasons.
“This is a great Club and I’m honoured to be a part of it and to captain the side.
“We have a great team here, the Club continues to improve and become more professional, and the future is only getting brighter for the South Sydney Rabbitohs.”
Rabbitohs Head Coach Jason Taylor was understandably delighted to retain the services of his front-rower ahead of this weekend’s game against Asotasi’s former club, the Bulldogs.
He said: “I enjoy working with him every day and I’m pleased that we can continue to build this team and this Club around players like him.
“Stability in your Club is very important, and a person like Roy gives us that, both on and off the field.
“It’s great to know he will be with us for the next four years.”
Souths currently lie 10th in the NRL, just a point off a play-off berth.