The singer will appear in campaigns that promote Emporio Armani Underwear and Armani Jeans collections in autumn/winter 2011-12.
The ads in which she appears were filmed in New York and will be released in September.
Other celebrities who have promoted the Italian brand include Victoria and David Beckham, Cristiano Ronaldo and Megan Fox.
Currently, Rihanna is a brand ambassador for Nivea on the occasion of its centennial.
A spokesperson for the brand said: “We are excited to have Rihanna supporting us in our celebration and building a new generation of fans.”