Australia's prison population has grown about 20 per cent over the past decade, a report says.

The Productivity Commission's report on government services on Friday revealed that the national adult imprisonment rate was about 190 per 100,000 people in 2014/15, compared to 158 in 2005/06.

Australia's prison population had grown steadily over the last 20 years. Credit:istock

The indigenous imprisonment rate per 100,000 Aboriginal and Torres Strait Islanders was higher, at 2196, compared to 139 per 100,000 non-indigenous people, it said.

Tasmania was the only state where the average daily prison population was slightly lower than five years ago, at 468 in 2014/15 compared to 474 in 2010/11.