The ad campaign is due to launch this month across the Capital 95.8 and One Network breakfast shows to support the product as a breakfast drink.
It will feature a "100% truth and nothing but the truth" competition, representing the 100% pure juice content of the drink, where listeners will be asked to identify which of the five breakfast show members is telling a story that is 100% true.
Two callers will be taken to air each day and the caller who identifies the 100% truthful story will be named winner.
Daily prizes include luxury weekend breaks to UK hotels, including the famous Gleneagles hotel in Scotland.
All the above activity will be supported via an on-air promotional campaign and significant online activity, including a 100% Pure Juices web page featuring a competition entry section, product logos and pictures, and hotlinks to the Ribena .
The deal was conceived and negotiated by Danielle Roe, GCap Media's client manager, and Nicolette Whittaker, planning manager, alongside GCap's sponsorship and promotions team and Ribena's media agency MediaCom.
Roe said: "It is fantastic to be working with Ribena again across Capital and The One Network. We worked closely to come up with something that would work well for radio and support all of the Ribena 100% Pure Juices brand values."
Ribena 100% Pure Juices launched last month and are available in blackcurrant and raspberry and blackberry blend.
A Ribena spokesperson said: ""We were really inspired by GCap's creative approach in addressing this brief. We wanted 100% juice to be a product that registered with consumers first thing in the morning and radios unique ability to allow modal targeting made it a key media for us to use."