The watchdog ruled against two ads for L'Oreal's Wrinkle De-Crease and Perfect Slim creams, which it said made misleading claims about their effectiveness.
Both ads claimed that the creams reduced wrinkles and cellulite after testing. The ASA asked an expert to consider the evidence and he found that the studies carried out by L'Oreal were limited and were not scientifically evaluated.
The ASA ruled that the ads should not be shown again unless the company could provide sufficient evidence to back up the claims.
In response to the rulings, L'Oreal claimed the Broadcast Advertising Clearance Centre had approved the ads.
Two weeks ago, the cosmetics company came under fire from the ASA for airing an ad for its Garnier Nutrisse hair dye, starring Davina McCall, during Saturday evening's episode of Big Brother, which McCall presents.