More than one offender a week is walking out of Leyhill open jail in South Gloucestershire.
Figures released for the period 2008 to 2009 show 58 inmates absconded.
Northavon MP Steve Webb said he supported the concept of open jails but it was important the "right sort of people" were being sent there.
A Prison Service spokesman said: "Prisoners located in open conditions have been rigorously risk assessed and categorised as being of low risk."
The Liberal Democrat MP added: "What I find alarming is that when somebody does walk out as happened a few weeks ago the police put out a notice saying, 'Don't approach this person he might be dangerous'.
"It they are that dangerous... what are they doing being sent to an open prison?"
The Prison Service said the number of people absconding from open prisons was at its lowest since centralised reporting of this type of incident began in 1995.
"Over 96% of prisoners who abscond are recaptured and returned to custody.
"On recapture the prisoner will be returned to a closed prison and referred to the police for consideration for prosecution for having been unlawfully at large," said a spokesman.
The figures, released under the Freedom of Information Act to the BBC, show 362 inmates absconded in England and Wales in 2008/9.