Glyn Travis, assistant secretary of the Prison Officers' Association said: "These films clearly shouldn't be freely available to prisoners to watch at any establishment.
"We've got adults who are locked up - some for serious sexual offences, some for violent or drugs offences - and the majority of films that will keep them entertained are completely and utterly inappropriate.
"It's difficult to try and address offending behaviour and get prisoners to lead law-abiding lives when you're showing them films which gratify their needs.
"It's very, very difficult. I think it's something that's never been addressed and it needs to be addressed to see what's appropriate."
Blockbuster Con Air, starring Nicolas Cage and featuring a plot with a group of dangerous prisoners taking control of a transport plane, is also among the films on offer to the 256 inmates.
Graphic 18-rated Menace II Society, which includes strong bloody violence and more than 300 uses of explicit terms, is on the list, along with gang war movie Last Man Standing.
Other films on the list include Harry Potter, Pirates of the Caribbean and Brokeback Mountain.
Mr Travis added: "it's wrong for any governor to allow such material in to his establishment for prisoners to watch when there's alternative entertainment available which doesn't gratify criminal activity.
"I think there's a balance between good sensible entertainment and entertainment which purely gratifies criminal activity."
The most recent report by HM Chief Inspector of Prisons on the Category C prison at Usk said inmates had "access to good library facilities with a good range of DVDs."
The vast majority of the prisoners - a total of 218, or 86.9 per cent - were inside for sexual offences.
All but eight of the remaining inmates had committed violent crimes.
Monmouth MP David Davies said he was shocked by the selection of DVDs available at the jail.
He said: "I would be extremely concerned to learn that videos, including violent sex scenes, are being put in to the library there. I'm really quite amazed.
"The whole purpose of Usk prison is to try and rehabilitate sex offenders. It's very hard to do that anyway, without them having access to violent or pornographic films."
Dr Alison White, a consultant clinical psychologist, said exposing prisoners to "the often glorified depiction of violence and sexual violence in films" was unlikely to be advantageous.
She said: "The literature base regarding sexual violence and watching films that portray sexual violence or video games that show violence or sexual violence would argue that it's not beneficial for offenders.
"Offenders have what we call cognitive distortion. They say things to themselves to make their offences seem okay, like 'She was asking for it', 'She was wearing a short skirt' or 'It seemed she was enjoying it'.
"By watching films which glamorise sexual violence or violence in any form it serves to reinforce their cognitive distortion.
"I guess the danger is when these things are freely accessible then the temptation is there, easily in their way, but that said these films are easily available on the outside."
A Prison Service spokesman said: "For prisoners over the age of 18, access to DVD players is linked to good behaviour and the earned privileges scheme.
"Access to players is only available to prisoners who have achieved the highest level on the scheme.
"Prison governors have discretion to prohibit the showing of any material they consider to be unsuitable."
The list of films in the prison's DVD library was released following a Freedom of Information request