The pair started out together in the entertainment business as children at the Mickey Mouse Club and the star recently tweeted Spears to congratulate her on her new album Femme Fatale.
Aguilera said to Parade: 'I haven't heard the whole thing in its entirety, I've been really hard on work on this show, but I am a huge supporter of her because both of our careers started off together and are still going strong.
'I think it's extremely important to be supportive of fellow artists and especially females, who often get pitted against each other and torn apart.
'As an old friend of mine from the Mickey Mouse Club, I think it's important at this stage in the game to really show my support.'