DeMarcus announced the happy news on his official Twitter account on Wednesday (January 25).
"Alright y'all, Ali and I have baby number two on the way!! Huge surprise but we're very excited," he tweeted.
Allison gave birth to the couple's 1-year-old daughter Madeline Leigh in December 2010.
Jay and Allison, a former Miss Tennessee, married in 2004 after meeting while filming the music video for Rascal Flatts' hit 'These Days'.
Rascal Flatts have earned an Academy of Country Music Award nomination for 'Vocal Group of the Year'.
Watch Rascal Flatts' 'These Days' music video below: