The pitch, which will be handled by the AAR, will begin early in the new year.
Clear Marketing Communications, the incumbent that worked on the campaign for the brand's launch in March 2007, will be asked to repitch for the business.
The move comes as the company prepares to increase its media spend in an attempt to grow audience in 2008.
Stuart Taylor, GMG Radio's group commercial director, said: "Clear Marketing Communications has done a great job across all our brands, and in particular the launch of Smooth across the UK.
"As we plan to increase our marketing spend on Smooth significantly over the next couple of years, and in particular across London, we want to ensure that we have the right creative marketing message that will provide us with the most powerful proposition for the brand."
Smooth Radio is aimed at listeners aged over 40 and is broadcast in six major regions across the UK.
GMG Radio extended the Smooth brand from its original two stations in London and the North-West when it rebranded the Saga Radio stations that it acquired inDecember 2006 under the Smooth banner.
In August, the company also put the media buying account for all of its 13 stations up for pitch. Also being handled by the AAR, it is expected to be concluded before Christmas.