Brazilian left-back Cassio has signed a two-year deal with Adelaide United the club has announced.
The 30-year old's previous contract was set to expire at the end of the season but the Reds have moved to secure him until the end of the 2012/13 season.
"I feel very good and very happy with this deal. My decision wasn't so hard because since I arrived here I have felt at home," Cassio said.
"The supporters, the club, my teammates, the new owners and the Adelaide people made my decision easy with how they have treated me, so that's why I chose to stay here."
Cassio, who joined the Reds in 2007, said he was currently feeling in the best shape of his career.
"I'm 30 years old at the moment and to be honest I feel much better physically than when I was 20. Don't ask me why, but I feel more confident, and after you get experience, you know where to run and you get smarter," he added.
"Football is my life and I know I have to keep performing well, playing good and giving Adelaide my best. This season has been great for me and I hope the next two can be even better."