A Forest Bank prisoner is the fifth inmate to die at the jail in just over a year.
The man died while in custody at the Salford prison on Sunday.
The Prisons and Probation Ombudsman will now investigate his death.
He is the fifth person to die at the Category B jail within 14 months. Prison bosses described the death as a “tragedy” but said they could not comment further while the matter is under investigation.
An HMP Forest Bank spokesperson said: “We can confirm there was a death in custody at HMP Forest Bank on Sunday, 1st September.
“Deaths in custody are a tragedy and our thoughts are with the family.
“As with any death in custody, there will be an investigation by the independent Prisons and Probation Ombudsman and therefore we are unable to comment further at this stage.”
This latest death comes just over two months after Raymond Lucy, 63, was found dead in his cell on July 11.
Mr Lucy - who suffered from chronic obstructive pulmonary disease (COPD) - was jailed for firing an air pistol during a drunken visit to his ex’s house.
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His loved ones visited him in prison a day before his death and told the M.E.N that he had appeared “grey” and “ill looking”.
Mr Lucy, from Chadderton, Oldham, was “too scared to sleep because he couldn’t breathe” and “had a fear of dying”, they said.
In February, Michael McDonagh, 27, was found unresponsive in his cell.
His mum Margaret said her son had been returned to prison following a serious driving offence and suffered with mental health issues.
Just a few months earlier, in September 2018, John Winchcole, 36, was also found dead in his cell.
And in July 2018, a 50-year-old unnamed man suffered a medical episode at the prison shortly before passing away.
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