Romeu, who has made 33 appearances for Chelsea since joining the club from Barcelona in the summer of 2011, was recently handed a new three-year deal by Chelsea manager Jose Mourinho.
The 22-year-old holding midfielder spent last season on loan with La Liga side Valencia, but will now have his first taste of Bundesliga action during the 2014/15 season.
A statement on Chelsea’s website read: “Oriol Romeu has today (Monday) joined Stuttgart on a season-long loan.
Stuttgart coach Armin Veh said: "Romeu has collected some experience in two top European leagues despite his young age and will help Stuttgart as it seeks to improve on last season's disappointing showing."
Veh, who led Stuttgart to the Bundesliga title in 2007, returned to the club this summer after a season in which they used three coaches and narrowly avoided relegation.