Chelsea announced Di Matteo's dismissal this morning.
Pardew, who will lead his own team into Europa League battle against Maritimo on Thursday evening, said: "I'm astonished, really. It just goes to show you how precarious we are as Premier League managers, and you can't take anything for granted.
"The shock that should be there for the fans and the media should sound something to the owner of that football club because I don't know if that's the ninth manager or whatever it is in so many short years. It's just not fair.
"As far as I am concerned, he has done absolutely nothing wrong. His philosophy was to perhaps change the look of the team, which he has tried to do - that doesn't happen overnight - and he's won two competitions in less than a year, so it's unbelievable.
"He should walk straight into another job - probably at someone else's misfortune, unfortunately."