The couple were attacked by the animal while walking along a public footpath through a livestock field in Stanford on Soar,
Nottinghamshire, on Friday afternoon.
The woman's 63-year-old husband died from his injuries at the scene of the incident, a spokesman for Nottinghamshire Police said. She managed to get to the nearby road just after the attack, where she flagged down a passing woman motorist who contacted emergency services.
She was taken to the Queen's Medical Centre in Nottingham, where she remained in a critical condition yesterday, the spokesman said.
The couple, from Glen Parva in Leicestershire, were believed to be seasoned walkers, and their two sons travelled to the East Midlands at the weekend to be at their mother's bedside.
The man's elderly parents had also been informed about his death, he said, but police were not yet in a position to release any identities because not all relatives had been informed.
It is not clear why the bull attacked the couple and, after being contained in a shed by its owner just after the attack, it was put down.
Detective Inspector Melanie Bowden said: "The couple's two sons and their other family members are absolutely devastated by this tragic incident. We are continuing to support them as they struggle to come to terms with what has happened."