The pair became treble winners at Inter in 2010, but the 29-year-old insists that will not take the focus off trying to beat Chelsea
Sneijder was part of the Portuguese's Inter side that won Serie A, the Champions League and the Coppa Italia to become the first Italian outfit to complete the treble.
On Wednesday the Dutchman, who helped seal Galatasaray's place in the last 16 with a 1-0 victory over Juventus, will once again meet Mourinho, but says the friendship will be forgotten about once he crosses touchline at the Turk Telekom Arena.
"What can I say about Mourinho?" Sneijder told Uefa's official club website. "We won this trophy together. But tomorrow is completely different, although outside the match we are friends.
"It's an important game, a game I want to win. I respect him a lot as we all respect Chelsea. We want to go all out for victory. A goal against Juventus won't change the world. It was a big achievement but we want more."
When asked to give his thoughts on the difference in coaching styles between current boss Roberto Mancini and Mourinho, he said: "I have to say that all coaches are different. I have had good ones and not-so-good ones. But those two, they are both good.
"I am very honest. Of course I have special feelings for Mourinho because we won the treble together. In our home games especially we are playing really well and tomorrow we'll be at home. Roberto Mancini and Jose Mourinho are different coaches in terms of personality but they are both good tactically."
The 29-year-old says Galatasaray will be full of confidence heading into the clash with the Blues.
The Turk Telekom Arena has been notoriously difficult for visitors, with Gala keeping six consecutive home clean sheets, including a 1-0 victory over fierce rivals Besiktas this weekend.
Mancini's men are also undefeated since their 6-1 loss to Real Madrid in September and Sneijder is hoping for the run to continue at the expense of Chelsea.
"This will be a very important game but also a very nice one to play," he continued. "It's amazing what we have achieved. Now we are here, we want more. It will be difficult.
"We feel confident as we had a good result at the weekend. We have to go for it and have to believe in it. Playing these games is good for the players at this level."