The outspoken Portuguese left the London club in 2007 after winning two Premier League titles and claimed an Italian scudetto in his first season at Inter last term.
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"I know Chelsea well but it doesn't mean it's easier. Sometimes it's more difficult because when you know so much about a team ... you can get into trouble," Mourinho told a news conference at Inter's training ground on Tuesday.
"I played against (former club) Porto with Chelsea the year after I left. It was my team, my players. It was not easy."
Chelsea coach Carlo Ancelotti moved in the opposite direction, leaving Inter's big rivals AC Milan in May to take over at Stamford Bridge.
"Carlo Ancelotti knows Inter very well. He has worked his whole life in Italian football so I don't think it's an advantage at all (that I know Chelsea)," Mourinho added before showering praise on John Terry, Frank Lampard and Didier Drogba.
Mourinho has been banned for three Serie A matches by the Italian league after his latest controversial caper, making a handcuffs gesture during Saturday's 0-0 draw with Sampdoria.
JOURNALISTS STUNNED
He refused to talk about the suspension but threatened to cause more bother when asked about Ancelotti being quoted as saying most of Italy would be supporting Chelsea on Wednesday.
"If he says that, it's because he knows, because someone told him or because he belongs to the clan," he said, without specifying what he meant.
While Italian journalists were left stunned by his use of the word clan given the country's mafia past, on the other side of the city Ancelotti was starting his news conference at his old San Siro haunt.
"I never said this (that non-Inter supporters in Italy will support Chelsea). It's not my style to say things like that. They've been opponents for many years and I will respect them tomorrow like I have always," Ancelotti said.
Ancelotti, who said he would not accidently walk into the home dressing room on Wednesday, wanted his team to concentrate and ignore tabloid stories about Terry and Ashley Cole.
"I was very surprised (English newspapers discussed players' private lives) but the surprise will end very quickly. However, I respect the culture," he said when asked if it was better in Italy where off-the-field activities are ignored.
"We are focused on these important games and nothing else. It won't change our motivation for this game what happened outside of our dressing room."
