Hilton, 29, was arrested shortly before midnight on Las Vegas Boulevard after police pulled over a vehicle that Hilton was in. The hotel heiress was not driving.
Public Information officer Marcus Martin said the vehicle was stopped after officers believed marijuana smoke was coming out of the car in front of the Wynn Hotel, where Hilton’s boyfriend, Cy Waits, operates a nightclub.
After a search of Hilton, cocaine was found in her purse, Martin said.
Hilton was booked into the Clark County Detention Center early Saturday morning but later released. The male driver of the car was arrested on DUI drug charges.
This was the third drug-related incident involving Hilton this summer.
In July, Hilton was held by police on the French island of Corsica and caught with less than a gram of marijuana in her purse but released without being charged.
Earlier in July, she was questioned by South African police at the World Cup after she was allegedly caught smoking marijuana. Her rep called it a "complete misunderstanding," and Hilton wasn't charged.
Her latest tangles with the law come three years after she went to jail for violating probation in an alcohol-related driving case.