Around 10,000 tablets, cocaine, alcohol and up to 30 mobiles have been seized at the jail today.
It's the largest single seizure of contraband in an Irish Prison, with a Garda investigation now underway.
The drugs and items recovered were individually wrapped with the intended recipient's name clearly labelled.
It's understood they were delivered into the Dublin prison through a supplier's vehicle.
A man has been arrested in connection with the seizure.
The man, who is in his 40s, is being questioned at Mountjoy Garda Station.
Gardaí say their investigation into the incident is currently ongoing.
