After a 10-match winless streak, the club officials have decided to take the harsh decision of sacking the 43-year-old manager.
The club confirmed the news on their official twitter handle and official website.
Middlesbrough's tweet read:
Aitor Karanka's tweets on parting ways with club read:
I'd also like to thank the fans for their support. This club will always hold a special place for me. 2/3— Aitor Karanka (@Karanka) March 16, 2017
I wish everyone connected with Middlesbrough Football Club the very best for the future. Up The Boro! 3/3— Aitor Karanka (@Karanka) March 16, 2017
The official statement from the club read: "Middlesbrough Football Club can today confirm the departure of Head Coach Aitor Karanka.
"Following discussions, both parties have agreed that it is in the best interests of the club to make this change.
The club would like to thank Aitor for all his hard work over the past three-and-a-half years and for the success we've had during that time. We wish him all the best for the future.
"Steve Agnew will step up from his role as assistant Head Coach to take control of first team affairs with immediate effect."
Karanka spoke on his sacking and said: "I'd like to thank Middlesbrough for a wonderful opportunity and the players, staff and all the people at the club who I have worked with.
"I'd also like to thank the fans for their support. This club will always hold a special place for me and I wish everyone connected with Middlesbrough Football Club the very best for the future."
Middlesbrough who gained promotion to top tier this season is currently placed at the 19th position in the league table and are on the verge of getting relegated again.
They have managed to secure only 22 points from 27 matches and are 3 points ahead of rock-bottom side Sunderland.