A 25-year-old prisoner at Armley jail in Leeds has been arrested on suspicion of murdering a fellow inmate.
The incident happened at Armley prison in Leeds
A man is being questioned following an incident at the prison on Friday, West Yorkshire Police said.
The inmate who died was named by the Prison Service as Shahid Aziz, 30, who was awaiting sentence after being convicted of criminal damage this week.
An independent investigation into the death is being carried out by Prisons and Probation Ombudsman Stephen Shaw.
Aziz had been awaiting sentence following a conviction for criminal damage at Leeds Crown Court on 31 March.
A police spokeswoman said: "A 25-year-old prisoner has been arrested on suspicion of murder following an incident at HMP Leeds on Friday.
"A 30-year-old prisoner was taken to Leeds General Infirmary shortly after 1200 GMT and died from injuries sustained."
The Prison Service confirmed there had been an incident involving two prisoners and that Aziz was subsequently pronounced dead at hospital.