Differences between the novels and TV series:

Blair's mother is a wealthy hostess in the book, she is a designer in the TV series.
In the book Blair has blue eyes while in the TV series, Blair has brown eyes.
Blair has a cat named Kitty Minky in the book. It is note worthy, though, that in the TV series, Roman, her father's lover, named their cat Cat, in reference to 'Blair's 가장 좋아하는 movie'
Blair's mom dresses very strangely in the books, whereas in the TV series, she is a fashionable woman.
In the books, Blair's father's male lover's name is Giles whereas in the TV series his name is Roman....