Prisoner-on-prisoner assaults more than doubled last year with an extra 25 incidents reported inside the Alexander Maconochie Centre. The number of serious assaults also increased by three.

The jail's population also swelled to 126.8 per cent last year, placing additional stress on those tasked with separating prisoners in the territory's only prison.

The figures were revealed in a report on government services released by the Productivity Commission on Friday.

Justice Minister Shane Rattenbury said he was concerned by the results and admitted it had been a challenging 12 months for corrective services.

"An over-populated facility provides operational challenges for corrective services which are further complicated by the high level of separation required in the ACT," he said.

Surging detainee numbers have put enormous pressure on overcrowded prisons across Australia, including the AMC, which has undergone urgent capacity upgrades to cope.

A 30-bed special care unit was opened in September to increase segregation inside the prison, although figures provided to Fairfax Media revealed it was at capacity one month later.

Mr Rattenbury said a larger 56-cell block to be completed later this year would provide prison staff with a greater ability to separate inmates at risk of assault.

The report also revealed inmates were less likely to participate in employment due to overcrowding, with the number of eligible inmates dropping from 69.6 per cent to 65.4 per cent.

Mr Rattenbury said the 4 per cent reduction was disappointing but insisted the government was committed to providing rehabilitation and a structured day at the jail.

Earlier this month, the government announced inmates would be put to work as part of a $9 million bakery and laundromat program designed to quell restlessness and aid rehabilitation.

The initiative comes after an ACT Auditor-General's report early last year, which found the prison was failing to meet its aim to provide structured days.

Only 41 per cent of prisoners were in some form of work, mainly in domestic-type tasks like cleaning, sweeping, emptying bins, and serving food.

There was some good news for the government, with the ACT retaining its top ranking for education and training within prisons. Slightly more than three quarters of inmates now participate in training courses each year, compared to the national average of 31.6 per cent.

"The ACT also had the second highest rate of completion for community corrections orders with 79.9 per cent," Mr Rattenbury said. "This is also an increase on the previous year at 77 per cent."

Close to 40 per cent of detainees released from prison during 2012-13 returned last year, which was a drop on the 41.9 per cent a year earlier.

Mr Rattenbury said this was the third consecutive drop and the ACT remained below the national average of 44.3 per cent.