The ACT Bar Association and Law Society both expressed concern at rising imprisonment rates in the territory, saying they are at odds with actual levels of crime.

The Legislative Assembly is looking at the way offenders are punished in the ACT through a wide-ranging inquiry into sentencing which has attracted 15 submissions so far.

The Law Society and Bar Association used their submissions to, among other things, raise concern over increasing imprisonment rates.

''The society is concerned with the recent upward trajectory in the rate of imprisonment,'' the Law Society wrote.

''The question to be answered is whether the rate reflects an underlying shift in the sentencing jurisprudence of the Territory, or whether it is fuelled by other factors.''

Prison is typically a last resort, where no other sentencing option is suitable.

The government acknowledged the imprisonment rate had increased in the ACT in the latest Justice and Community Safety Directorate annual report.

An unprecedented rise in prisoner numbers pushed the prison to capacity late last year, forcing authorities to urgently increase bed numbers.

The number of inmates rose by 40 per cent between January and October, the government says.

But Acting Attorney-General Joy Burch said the government was confident the criminal justice system was sentencing appropriately.

''Imprisonment rates across the majority of Australian states and territories have risen in recent years and as of June 30, 2013, the ACT had the lowest imprisonment rate in Australia,'' Ms Burch said.

Bar Association president Greg Stretton, SC, had also expressed concern over the increase in longer prison sentences.

''This increase seems to reflect a change in sentencing practice,'' Mr Stretton wrote. ''It is unclear why this has occurred given there has been no change to legislation that would warrant such an increase in the number and length of terms imposed.''

Mr Stretton also pointed to continuing high levels of recidivism in the ACT.

The directorate's latest annual report shows the proportion of detainees returning with a new correctional sanction within two years jumped from 40.8 per cent in 2009-10 to 46.64 per cent in 2010-11.

The Law Society echoed the concerns, saying the levels of re-imprisoned offenders in the ACT were the highest in the nation.

''Anecdotal reports have indicated a dearth of facilities made available to prisoners, in particular directed to education and qualification which may bear upon this rate of recidivism.''

''The society is concerned that a lack of implementation of rehabilitative strategies in the prison context undermines effective sentencing.''

Corrections Minister Shane Rattenbury said the government had a ''strong commitment'' to rehabilitation, shown by a new program introduced in the middle of last year.

That program provides former detainees with support for up to a year after release, to help them escape the cycle of recidivism.

''While still in its early stages, the ACT's extended Throughcare initiative has shown initial success in keeping recently released detainees in the community,'' Mr Rattenbury said.

The Bar Association also warned of an increasing prevalence of ''short, sharp'' sentences, saying an increasing number of prisoners were serving terms of two years or less.

''There is little evidence that imprisonment acts as an effective deterrent to future criminal behaviour,'' Mr Stretton wrote.

''The increasing resort to short sentences is likely to have the effect of exposing a greater number of people to the prison environment who might otherwise be punished in other ways.''