The incident happened just before 8 p.m. at the London West Hollywood Hotel.
Kardashian was holding an event to promote her new fragrance line when a young woman suddenly threw an entire bag of flour on her, according to E! Online.
A Los Angeles County sheriff's spokesperson said Kardashian declined to press charges. She cleaned up and continued with the event. The woman was detained by hotel security and later released.
There was no word on a motive, but E! Online said some bystanders heard the attacker mention something about fur.