The Egypt winger spent last season on loan at the Serie A club and the Blues confirmed that a deal has been struck to allow him to remain in the Italian capital.
Salah joined Chelsea in January 2014 - after impressing against them with Basle - but failed to pin down a permanent place before he was loaned out to Fiorentina and then Roma.
The 24-year-old becomes the second player to leave Stamford Bridge in the past two days after Baba Rahman joined Schalke on a season-long loan.
Source : PA
Source: PA