Sofia Vladimirovna Vassilieva is an American child actress of Russian descent from Minneapolis, Minnesota.

At the age of 7, she was discovered at the International Modeling and Talent Association (IMTA) in New York where she won the title of Child Actress and first runner-up Child Model Of The Year 2000.

In less than one year she had the part of Elena - the granddaughter of a retired Russian General in the episode "Deadline" of the CBS TV series The Agency (2001-2003).

At the age of 9 she played Cindy Brady in The Brady Bunch in the White House (2002) opposite Shelley Long and Gary Cole, and a little girl named Gina in Inhabited (2003) opposite Malcolm McDowell and The Bad Seed's former child actress Patty McCormack.

At the age of 9 and 10 she played the children's book heroine Eloise, in two made-for-television movies Eloise at the Plaza and Eloise at Christmastime directed by Kevin Lima, with Julie Andrewsas Nanny.

At 11, in May 2004, Sofia began playing the role of Ariel DuBois in Medium. She was a presenter of Family Feature Film on the Humane Society's 19th GenesisAwards in 2005. Vassilieva was nominated in 2005 for a SyFy Portal Genre Award as best young actor/actress for her role in Medium (but lost the award to Harry Potter's Daniel Radcliffe). She won a Young Artist Award in 2006 for best supporting actress in a TV Drama for her role in Medium.

Sofia is currently filming the screen adaptation of the novel My Sister's Keeper, written by Jodi Picoult alongside Cameron Diaz Jason Patric, and Abigail Breslin The film is directed by Nick Cassavetes. Sofia had to shave her eyebrows and long thick blonde hair to play the role of Kate, the girl suffering from leukemia.