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.
"I don't know if he said that," Mourinho said. "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.
"That is the last quote I have and it is an intelligent one."
Chelsea have been linked with former Barca and Samuel Eto'o, the Inter Milan striker who is reportedly available as his current club Anzhi Makhachkala cut costs.
Eto'o won the Uefa Champions League under Mourinho at Inter before moving to the previously big-spending Russians.
"I am always happy that somebody that worked with me previously is happy to be back and work with me again," Mourinho said.
"That is a good feeling that I have, when I read something that Samuel is keen.
"It is fantastic for us, but we are going to see what happens."
Mourinho has warned it could take time to get his squad as he wants it.
The Portuguese won two English Premier League titles in his first spell at Stamford Bridge and now wants to build the foundations for greater long-term success.
"This team is not just for tomorrow. It is a team for many, many years, so if in this moment we don't have the perfect squad, that is not a problem," he said.
"We work and we improve and the challenge is to improve the boys and improve the team every day.
"It is not a problem for us, we are not feeling this kind of pressure."
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