Dakota Fanning ad banned
The magazine ad for Oh Lola! perfume by fashion designer Marc Jacobs was likely to cause serious offence, it said.
It showed the actress wearing a thigh-length dress, with an oversized bottle of the scent resting between her legs.
The watchdog said the 17-year-old appeared younger than 16. Perfume maker Coty UK disputed the ASA's view.
The watchdog said it had received four complaints and the advert must not appear again.
A month ago, the ASA took part in a Downing Street summit to discuss how children could be protected from unsuitable images.
In its ruling the ASA said: "We considered that the length of her dress, her leg and position of the perfume bottle drew attention to her sexuality.
"Because of that, along with her appearance, we considered the ad could be seen to sexualise a child. We therefore concluded that the ad was irresponsible and was likely to cause serious offence."
Coty UK said it had not received any complaints about the advertisement featuring the Twilight actress which was published in "highly stylised" fashion publications including ES Magazine and the Sunday Times Style on 5 August 2011.
It did not feel the styling suggested the US model was underage.
It added it did not believe that readers of the magazines were likely to find the ad offensive because it was similar to many other "edgy" images which are featured.
It told the ASA the giant perfume bottle - shaped like a vase containing a flower in bloom - was "provoking but not indecent".
Source:bbc