The French cosmetics giant believes that Fonda, 68, will reflect its relevance to the mature-women market.
The Age Re-Perfect range is specifically designed to address the physiological needs of women over the age of 65.
Fonda, who has won two Oscars and an Emmy, is renowned for her attitude toward 'real beauty' and embracing the ageing process. Last October, she refused to allow photographs of her to be retouched when she became the oldest woman to appear on the cover of Good Housekeeping magazine.
Other celebrities who endorse L'Oreal products include Andie MacDowell and Claudia Schiffer.