Pellegrino only took up the reins in May, but Los Che - currently 11th in the Primera Division standings but just four points off a Champions League place - decided to dispense with his services after the 5-2 defeat against Real Sociedad at the Mestalla.
"We have been exchanging views, and we made the decision to dismiss Mauricio Pellegrino," president Manuel Llorente said.
The defeat followed a humiliating 4-0 loss at Malaga last weekend and, although they have qualified for the knockout stages of the Champions League, this reverse was one too many to take.
No permanent replacement has been named, but former player Salvador Gonzalez, known as Voro, who has been part of the set-up at the club since 2008, will take temporary charge.
"For the time being, there is not a (permanent) replacement," sporting director Braulio Vazquez said on the club's website. "Voro will take charge of the team at this time and I believe that is an important decision.
"What is important is to succeed, regardless of the background of the coach."
He added: "If you look at the future of the team, you can understand that in this game we have not been good, but the progression of the team was not right.
"I want to emphasise that Mauricio has gone, but it is the responsibility of all."
Llorente spoke of his disappointment of having to dismiss Pellegrino, saying he and the players should take some of the blame for the club's recent failings.
"As you can all think, it is painful," he said. "But we have to think about the scope of our responsibility, and we have to take such decisions.
"In all the time I've been at Valencia CF, this is the first time we removed a manager. I feel responsible - I'm the president.
"It is not only down to Mauricio Pellegrino, but it's my responsibility, the players... and I believe that all those who direct the club are responsible.
"And we have it to make decisions. And these (decisions) hurt a lot, as is in this case because I have always had a very high opinion of Mauricio.
"The intention that we have is to get the team into the Champions League (again)."
Valencia was Pellegrino's first job in management after previous spells as assistant coach at Liverpool and Inter Milan under former Los Che boss Rafael Benitez.
The 41-year-old Argentinian made 140 league appearances for Valencia during a six-year spell from 1999 to 2005.