The Advertising Standards Authority (ASA) received 22 complaints that the ads were socially irresponsible because the model, shown posing in outfits including swimwear, a dress and a a tank top and skirt, looked unhealthily thin.
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Nasty Gal said the model was a UK size eight and had a body mass index (BMI) within the healthy range for an adult woman.
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Ad clearance agency Clearcast said the model weighed 9st 8lb (60.9kg) and was 5ft 10in (178cm) tall with a BMI of 18.8, which sat "well within" the healthy weight and BMI range in accordance with NHS guidelines.
The ASA said the model generally appeared to be in proportion but there were specific scenes which drew attention to her slimness because of her poses, including one which prominently showed her ribcage.
The ASA said: "We considered that the model appeared unhealthily underweight in those scenes and concluded that the ads were therefore irresponsible."
It ruled that the ads must not be broadcast again in their current form, adding: "We told Nasty Gal to ensure that the content in their ads were prepared responsibly."