The fashion designer and wife of Manchester United footballer Wayne Rooney sported the new designs in a photoshoot for the retailer.
"I always consider different shapes when I'm designing," Coleen said.
"My collection is a really wearable but gorgeous selection of bikinis, tankinis and kaftans so women can show off or cover up however they choose."
The collection will go live on March 8 via the phone or the Littlewoods website and prices range from £15 to £40.
Littlewoods womenswear design director Rebecca Elderfield said: "Coleen is famous for her curves and always looks fantastic on the beach.
"We are incredibly excited that she has designed a swimwear collection for us, aimed at real women with real curves, and has chosen to model it herself."
Rooney became a style ambassador for Littlewoods in June 2010 and designed her first range for the company in Spring-Summer 2011.
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Watch Coleen Rooney talk about her favourite looks from her new Spring 2012 range for Littlewoods below: