The versatile Brazil international has been linked with a big-money move to Barcelona but Mourinho is adamant the 26-year-old will not be leaving Stamford Bridge.
Mourinho, who returned to the London club for a second spell this summer, told BT Sport: "No chance he is going to leave. He is a player we want to keep.
"He is a player with four years (on his) contract, he just signed a contract last year.
"We like him. He is an important player for the club and the club is not ready to sell him for any price."
Luiz joined the Blues from Benfica in 2011 and signed a new five-year contract last September.
There have been reports recently claiming Luiz has told the club of his desire to join Barca but Mourinho says he is not aware of that.
He said: "I don't know if he said that. What I can say is that he is not going to.
"The last quotes I read were Luiz saying he is not speaking about clubs when he is with the national team, which is a fantastic quote that I appreciate.
"When they are with the national team they are national team players, they are not club players.