Spears brought her 'Femme Fatale' tour to the Staples Centre on Monday night after kicking off the US leg of her world tour on June 16.
Kardashian attended the show - which was opened by Nicki Minaj - with her sisters Kylie and Kendall Jenner and Pussycat Dolls creator Robin Antin.
"Seriously u guys, tonight @britneyspears just had the best concert ever! She killed it in LA! Proud of u doll ;-) must see concert! (sic)" she wrote on Twitter.
Hilton, who has been photographed partying with Spears in the past and recently told reporters the pair were still friends, was another famous face in the audience, arriving at the Staples Centre with friends including sister Nicky Hilton.
"Britney Spears's concert rocked! So much fun! She looked so stunning! So proud and happy for her! :)" she wrote on Twitter.
"Loves it! @BritneySpears performing @Rihanna's song S&M! Her outfits are amazing! Who did the costume design for her tour? Love!"
Nicky Hilton agreed, writing on her own feed: "@BritneySpears show was amazing! She looked and sounded beautiful! Great concert!"
Spears was joined on stage by support act Minaj for her encore performance of 'Till The World Ends' following a 22-track setlist, which included hits 'Hold It Against Me', 'Womanizer' and 'Toxic'.
Spears's new music video for upcoming single 'I Wanna Go' is scheduled to be released tomorrow. It marks the third release from her Femme Fatale album.
Watch Britney Spears and Nicki Minaj perform 'Till The World Ends' below: