With the Old Trafford post vacant, the Chelsea manager says "no job would move me" from Stamford Bridge.
The Portuguese was considered one of the favorites to replace Sir Alex Ferguson last year, but David Moyes was chosen to take the position and Mourinho opted to return to former club Chelsea.
At a news conference Friday ahead of Chelsea's match against Premier League leader Liverpool, Mourinho said: "Of course not, I don't know how somebody can think about it.
"I left Real Madrid to come specifically to Chelsea. I signed a four-year contract. I told Chelsea they never have to worry about me because I never want to leave.
"So I'm here as long as they want me to stay. No job would move me from Chelsea."
Manuel Pellegrini — manager of United's rival Manchester City — has expressed sympathy for Moyes, pointing to the scale of the task the former Everton boss faced when replacing Ferguson.
"I think he is a very good manager, that is why Manchester United chose him to continue the work that Sir Alex Ferguson did for so many years," Pellegrini said. "But I don't know the reasons they have. It is always not good for the club to sack a manager who has a contract who is just starting his work — and it's very difficult to work after Alex Ferguson."