The Serbian midfielder has been a key player for the Blues since his arrival at Stamford Bridge from Benfica in January.
Ahead of Tuesday's visit of Maribor in the Champions League, Mourinho believes that the 26-year-old's evolution mirrors that of the team's.
"He adapted well last season, but this season he has much more understanding of what we want from him, much more confidence," the Portuguese told reporters. "He's a good player surrounded by good players. We're so happy with him, obviously."
Matic has scored two goals in 11 games for Chelsea so far this season.