Beyoncé welcomed her first child with husband Jay-Z on Saturday in New York.
Knowles tweeted about the birth of the baby girl on Sunday, writing: "The most beautiful girl in the world.
Beyoncé first announced her pregnancy in August at the MTV Video Music Awards.
In November, Knowles revealed that she has been passing on "mommy tricks" to her big sister.
Knowles is mother to 7-year-old son Julez.