Advertising Standards Authority decided to ban the two advertisements after complaints that the digitally altered images made the stars' skin appear more flawless than they originally are, the Daily Mail reported.
"On the basis of the evidence we had received we could not conclude that the ad image accurately illustrated what effect the product could achieve, and that the image had not been exaggerated by digital post production techniques," the agency said on the Julia Roberts picture.
The complaints against the ad campaign of the French cosmetics giant were brought by MP Jo Swinson, who argued that airbrushing creates a false impression of beauty.
She claims the results put pressure on women and young girls who compare themselves unfavourably to the unrealistic images.
Roberts ad showed the actress in a two-page magazine spread for Teint Miracle foundation by Lancome, one of L'Oreal's make-up brands. The ad claimed the foundation "recreates the aura of perfect skin".
L'Oreal admitted that certain "post production" techniques had been used on the image of the actress. But it insisted the picture was an accurate representation of her "naturally healthy and glowing skin".
The company also faced fire over its image of Turlington in a magazine ad for The Eraser foundation, from its Maybelline brand.
L'Oreal said the image had been digitally re-touched to "lighten the skin, clean up make-up, reduce dark shadows and shading around the eyes, smooth the lips and darken the eyebrows".
However, again, it insisted that the image was an accurate reflection of the benefits of the product.
The ASA was not convinced, ruling the images could not be used again in their current form.
