The device was found on Sunday and officials have said it is not thought to be terror related.
Police have confirmed they were called to the Warrington prison on Sunday evening.
In a statement the Ministry Of Justice said
""There was an incident at HMP Risley on Sunday 12 November. There was no threat to the public or those within the prison.”
“The matter has been referred to the police and it would be inappropriate to comment further.”
It's thought the prison was on lock down for a time and that no prisoners were hurt.
A Cheshire Police spokesperson said
"Police were called at 4.05pm on Sunday, 12 November to reports of a potentially explosive device at HMP Risley, Warrington Road.
"The device was dismantled and it is not believed to be terrorist related.
Enquiries are ongoing."