Omeruo, who started all four of Nigeria's matches in this summer's World Cup in Brazil, made 14 appearances for the Championship side after joining on loan for the second half of last season.
Earlier this month Middlesbrough boss Aitor Karanka - formerly Jose Mourinho's assistant at Real Madrid - confirmed he expected Omeruo to return to the Riverside Stadium for the coming campaign.
And on Sunday the 20-year-old - who can play as a center back or right back - took to Twitter to reveal his excitement at returning to the North East to work with Karanka once more.
Holiday is finished. . Almost time for work again.. happy to be re joining boro for a new season. . http://t.co/UEZQjj5lYR— kenneth omeruo (@omeruo22) July 20, 2014