Leslie, a 24-year-old Adelaide native, was allegedly caught carrying two Ecstasy tablets after police raided the Vertigo Cafe during a dance party at GW Cultural Park, early on Saturday morning, said Col. Bambang Sugiharto, from the police narcotics division on Bali Island.
Ecstasy is a synthetic drug, considered part hallucinogen and part amphetamine.
Under Indonesia's tough drug laws, a person found guilty of narcotics possession faces up to 10 years in jail. But Leslie is likely to get only a few months behind bars if convicted because she was caught with a small amount.
Leslie is being detained at police headquarters, where the Bali Nine -- a group of Australians picked up for attempting to smuggle heroin -- were held earlier in 2005.
She is the latest in a string of foreigners to be detained during a police crackdown on illegal drugs across the country. Employing surprise raids and on-the-spot drug tests, authorities have netted scores of Indonesian celebrities and foreign tourists.
Last week, a Bali court sentenced Australian businessman John Pyle to five months in jail for possessing a small amount of hashish.
Schapelle Corby was sentenced to 20 years in prison in May for smuggling 4.2 kilograms of marijuana onto Bali. Corby's defense team claimed she was likely a victim of an Australian drug ring involving corrupt baggage handlers who failed to retrieve marijuana planted in her surfboard bag before it was transferred to an international flight in Australia.
The Bali Nine - eight Australian men and one woman, ages 19-27 - were arrested in April for allegedly trying to smuggle nearly 11 kilograms of heroin out of Indonesia. Their trial is expected to start in September.