Pratt, who appears on U.S. show The Hills, was pulled over by police in Hollywood on 18 October (09) and taken into custody after failing a breathalyser test.
The blonde was just over the 0.8 legal limit for California after a second breath test registered at 0.9, according to TMZ.com.
Pratt, who has promised to take "full responsibility" for her mistake, was formally charged on Wednesday (28Oct09).