Germany international Andre Schurrle, former Vitesse midfielder Marco van Ginkel and ex-Fulham goalkeeper Mark Schwarzer have all made the switch to Stamford Bridge during the current transfer window.
The Portuguese manager told the club's website: "Andre Schurrle is still so young but he already has great history because he plays in his national team, he has played Champions League and he played three complete seasons for Leverkusen.
"Marco van Ginkel is one of the best prospects. He is not yet like Schurrle, close to being a finished product, but he is a player with great potential.
"Mark Schwarzer is what we need. With Mark we have a goalkeeper who has played an incredible number of matches in the last 10 years in the Premier League and he is more than ready for this."
Mourinho re-joined Chelsea last month after ending his three-year reign at Real Madrid.