The ACT Magistrates Court proved the lowest percentage of defendants guilty in the nation last financial year, new data shows.

The Australian Bureau of Statistics released a set of data collected from courts across Australia for 2011-12 on Thursday.

The data, which can be skewed by the ACT's relatively small population, shows the ACT Magistrates Court proved 64 per cent of finalised defendants guilty in 2011-12, the lowest of any state or territory.

That figure includes defendants who pleaded guilty or were found guilty.

It compares with 94 per cent in Western Australian magistrates courts and 91 per cent in Queensland magistrates courts.

The next lowest percentage was recorded in the Northern Territory, where 72.6 per cent of finalised defendants were proven guilty.

The statistics also show the ACT Supreme Court proved the second lowest percentage of defendants guilty in the country.

Only 69.8 per cent of finalised defendants were proven guilty in the ACT Supreme Court, just above South Australia, which proved 65.2 per cent of defendants guilty.

The Supreme Court also acquitted 9 per cent of finalised defendants, the equal highest proportion in the nation, but only just above the national average of 8 per cent.

Six per cent of Australia's guilty defendants were sent to prison, the ABS found.

In the ACT Magistrates Court, 9 per cent of guilty defendants were sentenced to jail time, higher than the national average of 5 per cent.

As expected, the proportion sent to correctional institutions by the Supreme Court was far higher.

More than 63 per cent of defendants proven guilty in the Supreme Court were sentenced to jail time. That was just under the national average of 65 per cent.

The ABS also found the total number of defendants finalised through all of Australia's courts had decreased by 11 per cent since 2006-07.

There were 572,251 defendants in total for 2011-12, the vast majority of whom were male, and more than 40 per cent of whom appeared on traffic offences.