A 28-year-old man was injured today at Mountjoy Prison in the fourth attack on an inmate at the jail in the past week.
The prisoner was attacked as he left the A Wing exercise yard at around noon.
He was brought to hospital where he is being treated for four stab wounds to the "mid-body", a Prison Service spokesman said, adding that his injured were not life-threatening.
It is understood the victim is Wayne Callaghan, from Clondalkin in west Dublin, who is serving a five-year sentence for possession of a firearm, dangerous driving and reckless endangerment.
Gardaí are investigating the attack which is not believed to be linked to other attacks in the jail this week.
Last evening, a 21-year-old man was stabbed at around 7pm. The Prison Service spokesman said the victim alerted prison officers that he had been attacked in an exercise yard.
He was initially treated at the prison before being transferred to the Mater Hospital where he was treated for a stab wound to the body and two to the arm. His injuries were not life-threatening.
The attacks come in the same week that 21-year-old Gary Douch was murdered in a communal cell in the jail.
An independent inquiry into the death of the Tallaght man, was launched after he was beaten to death while in a cell with six other inmates. Douch was put in the special holding cell because he had requested protection.
Gardaí and prison staff have begun separate investigations into all the incidents at the prison but the former senior civil servant Michael Mellett is heading an independent inquiry ordered by Minister for Justice Michael McDowell.
A 23-year-old man from Coolock was arrested hours after Douch was found dead in the cell at 6.30 on Tuesday morning. He was later released without charge.
It is understood the chief suspect in the killing had been held in several jails in recent times and had also been assessed at the Central Mental Hospital before being returned to Cloverhill last week and transferred to Mountjoy on Sunday.
Douch was a drug addict serving three years for assault and possession of drugs.
Last Friday, Goodwill Udechukwu, was attacked in an exercise at Mountjoy by a mob of around 10 men.
It was Udechukwu's first day in the prison after being given a life-sentence the day before for murdering his wife with a lump hammer.
The Irish Prison Officers Association had recently expressed concern about overcrowding at Mountjoy and The Irish Timesreported this week that 527 inmates were being held at the prison - 57 more than its operational capacity.
An inmate was also attacked in Cork Prison this week.
Thomas Kennedy (21), was in remanded in custody two weeks ago after being accused of murdering 19-year-old Sheola Keaney. He was attacked in the prison last Sunday and taken to hospital for treatment on facial injuries.