Joao Maria de Souza had been in bed with his wife Leni when the animal fell through the ceiling of their home in Caratinga, southeast Brazil, narrowly missing his wife.
The cow is believed to have escaped from a nearby farm and climbed onto the roof of the couple's house, last week.
The corrugated roof immediately gave way and the heavy animal fell eight feet onto de Souza's side of the bed.
Reports said his wife and the cow both escaped unharmed.
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However, hours later, he died from internal bleeding while still waiting to be seen by doctors, his family said.
"Being crushed by a cow in your bed is the last way you expect to leave this earth," de Souza's brother-in-law Carlos Correa told Brazil's Hoje em Dia newspaper.
"I didn't bring my son up to be killed by a falling cow," his grieving mother, Maria de Souza, told Brazil's SuperCanal TV channel.
Police have launched an enquiry into the bizarre death. The owner of the cow could be charged with involuntary manslaughter, the report said.