Public servants in ACT government agencies charged $6.3 million of supplies to their official credit cards last year, an audit shows.

The ACT Auditor-General's report, tabled in June this year, examined credit card use across all territory public agencies last year, finding the ACT public service charged between $456,000 and $599,000 a month to credit cards in 2015.

An audit has found the ACT Government's credit card bill hit $6.3 million last year.

It found the Education, Health and Justice and Community Safety directorates were the three biggest spenders, but some smaller agencies were more frequent credit card users.

The audit also revealed a marked discrepancy between the size of individual agencies and the number of credit cards they had issued to them.