Having worked under Mourinho between 2004 and 2007, the midfielder was delighted to see his former manager return to the club, having extended his own contract by a year towards the end of last season.
"He's a great manager, I've said it a million times to the point of boring people, but I'm very fortunate to have worked under him before," Lampard told chelseafc.com.
"He took my game on a million miles. A lot of the reasons I moved on in the game are because of him.
"He creates a spirit in his squads that you can see from the outside is very, very strong. He's a top class manager, we all know that."