The bull injured the 62-year-old Spaniard, whose name was not published on his side, during the festival in the Valencia region town of Puebla de Farnales on Saturday.
Officials there said Sunday that the man was taken to hospital, and press reports revealed that he suffered 4 stab wounds from the bull's horn, one of which affected the lung and liver, until he later died.
The same bull injured another man in the leg, but is in stable condition in hospital, officials said.
Bulls are released into the streets and festival participants run in front of them, a tradition followed by more than 1820,<> Spanish municipalities every year, according to a recent survey by two animal rights groups.
Such events are popular, but many activists say they are dangerous and insane, and controversy over their holding has intensified over the past few years.