The actor believes this year has been great for Bullock, who had some tough time following her 2010 divorce from husband Jesse James, who cheated on her.
Speaking about his old friend, Clooney, who was in a playful mood, said Bullock did not want him to reveal that they are old friends.
"Isn't she great? I've known Sandy for - she doesn't want me to say - over 25 years," Clooney, 52, told People magazine while attending the AFI Film Festival premiere of 'August: Osage County'.
"She's a really dear friend. So watching how this year has gone for her - and she's had tough years before - has been great."
When asked how she balances motherhood and her career, Clooney joked, "I don't balance motherhood. I got a kid here, a drink here." But he added: "She does it all. She's a great mom.