The 51-year-old Portuguese had desperately tried to sign Gerrard for Chelsea in 2005 but the midfielder had opted to remain at his boyhood club.
Now after nearly a decade, Gerrard has decided to end his 17-year-old Liverpool career and move to MLS side Los Angeles Galaxy after the end of this season.
On being asked whether not being able to sign Gerrard for Chelsea was the biggest disappointment of his career or not Mourinho replied: "Yes, but I have another one when I was trying Lampard to Inter. I was almost there and it didn't happen too. I had a couple of disappointments and that's normal in football."
The former Real Madrid boss feels that the midfielder would have been a good fit at Stamford Bridge.
"He (Gerrard) is a historical player for Liverpool, a historical player for the Premier League and an opponent I have always admired and respected," Mourinho told ESPN.
"We did everything to try (to sign him) and it was almost there. I was dreaming of (Claude) Makelele, Gerrard and (Frank) Lampard in midfield. We were playing in a proper triangle without a number 10 and playing Maka in front of the defenders."
Despite admitting that he and the rest of the Chelsea hierarchy had dreamed of signing Gerrard, Mourinho claims that he always knew that the 34-year-old would never leave Anfield.
"Me, Mr Abramovich and (former Chelsea chief executive) Peter Kenyon at that time, we dreamed of that. His people were open to him joining a top side like Chelsea. But to me personally he never said he would come. Never. He (Gerrard) was always a red and I think the decision was right."
"I love this quote when he was saying in his life he would never score a goal against Liverpool. I love these words. I understand why he was - almost, almost, almost - coming to Chelsea. But he didn't and I respect that a lot."
Gerrard's costly slip against Chelsea at Anfield that resulted in the Reds surrendering the Premier League title last season has been subject to a lot of mockery, with some Blues fans are making a song of the whole incident.
But Mourinho feels that the Chelsea fans are showing a lack of respect to Gerrard by regularly singing that song at Stamford Bridge.
"The song that my fans have I don't like at all," Mourinho added. "A couple of times it is good fun but to go and go and go, especially with a player like him who deserves respect, I don't think you don't need that. We have so many other songs, you don't need that one."