Down made his debut for the Blues in 2007 before suffering a broken leg against Racing Metro in 2011. He has since recovered to become an integral part of the Cardiff Blues pack.
"It was an easy decision to sign again with the Blues," said the lock.
"It's my hometown region. I've played all my rugby here and come through the Academy system so I always wanted to stay."
The age grade product has featured regularly this season and started in last weekend's Heineken Cup clash with Toulon.
"It's been really positive on a personal note to play a lot of rugby this year having picked up injuries in previous seasons," added Down.
"It's an important thing for any player to get a run of games to get some consistency and this is the first season I've been able to do that in a Blues shirt."
Looking to the future, Down, who was called up for Wales last year, believes good things lie ahead for both himself and the Blues.
"Certainly in seasons to come I can't see any reason why we can't challenge for honours with the talent we have, if we can keep hold of quality players," he argued.
"It was a real honour and privilege to be called up to the Wales squad, even though it was only for a short time.
"To contribute to the training was brilliant and to be in that environment made me want it more."