| 31 Aug 17 | M. Johnson Marvin Johnson |  Oxford UnitedOXF | → |  MiddlesbroughMID | Undisclosed |
| 31 Aug 17 | C. Johnson Callum Johnson | MiddlesbroughMID | → |  Accrington StanleyACCR | Loan |
| 30 Aug 17 | R. Shotton Ryan Shotton |  Birmingham CityBIR | → | MiddlesbroughMID | Undisclosed |
| 11 Aug 17 | L. Baker Lewis Baker |  ChelseaCHE | → | MiddlesbroughMID | Loan |
| 11 Aug 17 | L. Baker Lewis Baker | ChelseaCHE | → | MiddlesbroughMID | Loan |
| 10 Aug 17 | M. de Roon Marten de Roon | MiddlesbroughMID | → |  AtalantaATA | Undisclosed |
| 10 Aug 17 | M. de Roon Marten de Roon | MiddlesbroughMID | → | AtalantaATA | Undisclosed |
| 04 Aug 17 | H. Chapman Harry Chapman | MiddlesbroughMID | → |  Blackburn RoversBLK | Loan |
| 04 Aug 17 | G. Ramírez Gastón Ramírez | MiddlesbroughMID | → |  SampdoriaSAM | Undisclosed |
| 04 Aug 17 | G. Ramírez Gastón Ramírez | MiddlesbroughMID | → | SampdoriaSAM | Undisclosed |
| 28 Jul 17 | A. Fletcher Ashley Fletcher |  West Ham UnitedWHU | → | MiddlesbroughMID | 6,500,000 |
| 28 Jul 17 | A. Fletcher Ashley Fletcher | West Ham UnitedWHU | → | MiddlesbroughMID | 6,500,000 |
| 22 Jul 17 | D. Randolph Darren Randolph | West Ham UnitedWHU | → | MiddlesbroughMID | 5,000,000 |
| 22 Jul 17 | D. Randolph Darren Randolph | West Ham UnitedWHU | → | MiddlesbroughMID | 5,000,000 |
| 21 Jul 17 | C. Stuani Cristhian Stuani | MiddlesbroughMID | → |  GironaGIR | Undisclosed |
| 21 Jul 17 | C. Stuani Cristhian Stuani | MiddlesbroughMID | → | GironaGIR | Undisclosed |
| 18 Jul 17 | C. Cooke Callum Cooke | MiddlesbroughMID | → |  BlackpoolBLP | Loan |
| 17 Jul 17 | B. Assombalonga Britt Assombalonga |  Nottingham ForestFOR | → | MiddlesbroughMID | Undisclosed |
| 14 Jul 17 | C. Roberts Connor Roberts |  Swansea CitySWA | → | MiddlesbroughMID | Loan |
| 14 Jul 17 | C. Roberts Connor Roberts | Swansea CitySWA | → | MiddlesbroughMID | Loan |
| 14 Jul 17 | G. Miller George Miller |  BuryBURY | → | MiddlesbroughMID | Undisclosed |
| 13 Jul 17 | M. Braithwaite Martin Braithwaite |  ToulouseTOUL | → | MiddlesbroughMID | Undisclosed |
| 13 Jul 17 | M. Braithwaite Martin Braithwaite | ToulouseTOUL | → | MiddlesbroughMID | Undisclosed |
| 11 Jul 17 | J. Husband James Husband | MiddlesbroughMID | → |  Norwich CityNOR | Undisclosed |
| 10 Jul 17 | B. Guzan Brad Guzan | MiddlesbroughMID | → |  Atlanta United FCATL | Allocation |
| 10 Jul 17 | B. Guzan Brad Guzan | MiddlesbroughMID | → | Atlanta United FCATL | Allocation |
| 07 Jul 17 | B. Espinosa Bernardo Espinosa | MiddlesbroughMID | → | GironaGIR | Undisclosed |
| 07 Jul 17 | J. Howson Jonathan Howson | Norwich CityNOR | → | MiddlesbroughMID | Undisclosed |
| 07 Jul 17 | C. Christie Cyrus Christie |  Derby CountyDER | → | MiddlesbroughMID | Undisclosed |
| 06 Jul 17 | A. Barragán Antonio Barragán | MiddlesbroughMID | → |  Real BetisBET | Loan |
| 06 Jul 17 | A. Barragán Antonio Barragán | MiddlesbroughMID | → | Real BetisBET | Loan |
| 01 Jul 17 | J. Fryer Joe Fryer | MiddlesbroughMID | → |  StevenageSTE | Loan |
| 01 Jul 17 | J. Rhodes Jordan Rhodes | MiddlesbroughMID | → |  Sheffield WednesdaySHW | Undisclosed |
| 01 Jul 17 | V. Fischer Viktor Fischer | MiddlesbroughMID | → |  MainzMAIN | Undisclosed |
| 01 Jul 17 | J. Rhodes Jordan Rhodes | MiddlesbroughMID | → | Sheffield WednesdaySHW | Undisclosed |
| 01 Jul 17 | V. Fischer Viktor Fischer | MiddlesbroughMID | → | MainzMAIN | Undisclosed |
| 31 Jan 17 | A. Jakupovic Arnel Jakupovic | MiddlesbroughMID | → |  EmpoliEMP | Undisclosed |
| 31 Jan 17 | J. Rhodes Jordan Rhodes | MiddlesbroughMID | → | Sheffield WednesdaySHW | Loan |
| 31 Jan 17 | J. Rhodes Jordan Rhodes | MiddlesbroughMID | → | Sheffield WednesdaySHW | Loan |
| 31 Jan 17 | C. De Peña Carlos De Peña | MiddlesbroughMID | → |  Real OviedoOVI | Loan |
| 31 Jan 17 | C. Cooke Callum Cooke | MiddlesbroughMID | → |  Crewe AlexandraCREW | Loan |
| 31 Jan 17 | M. Kitching Mark Kitching | MiddlesbroughMID | → |  RochdaleROCH | Undisclosed |
| 31 Jan 17 | A. Guédioura Adlène Guédioura |  WatfordWAT | → | MiddlesbroughMID | Undisclosed |
| 31 Jan 17 | A. Jakupovic Arnel Jakupovic | MiddlesbroughMID | → | EmpoliEMP | Undisclosed |
| 26 Jan 17 | J. Burn Jonathan Burn | MiddlesbroughMID | → |  Bristol RoversBRI | Loan |
| 20 Jan 17 | B. Morris Bryn Morris | MiddlesbroughMID | → |  Shrewsbury TownSHR | Free |
| 18 Jan 17 | E. Nsue Emilio Nsue | MiddlesbroughMID | → | Birmingham CityBIR | Undisclosed |
| 18 Jan 17 | E. Nsue Emilio Nsue | MiddlesbroughMID | → | Birmingham CityBIR | Undisclosed |
| 18 Jan 17 | P. Bamford Patrick Bamford | ChelseaCHE | → | MiddlesbroughMID | Undisclosed |
| 09 Jan 17 | D. Nugent David Nugent | MiddlesbroughMID | → | Derby CountyDER | Undisclosed |
| 09 Jan 17 | D. Nugent David Nugent | MiddlesbroughMID | → | Derby CountyDER | Undisclosed |
| 05 Jan 17 | Mikael Soisalo | TXXTampereTampere | → | MiddlesbroughMID | Undisclosed |
| 05 Jan 17 | J. de Sart Julien de Sart | MiddlesbroughMID | → | Derby CountyDER | Loan |
| 05 Jan 17 | T. Mejias Tomas Mejias | MiddlesbroughMID | → |  Rayo VallecanoRAY | Loan |
| 05 Jan 17 | J. de Sart Julien de Sart | MiddlesbroughMID | → | Derby CountyDER | Loan |
| 04 Jan 17 | R. Gestede Rudy Gestede |  Aston VillaAVL | → | MiddlesbroughMID | Undisclosed |
| 04 Jan 17 | R. Gestede Rudy Gestede | Aston VillaAVL | → | MiddlesbroughMID | Undisclosed |