Two out of every three women who take maternity leave in the public service do not receive promotions after they return to work, according to a new study.

The Australian Public Service Commission study looked at the progression of female public servants who took maternity leave in  2000-01.

It found that by June last year 65 per cent of those that took the leave had not been promoted, News Limited reported today.

That compares to 42 per cent of women without children who had not received a promotion in the same period.

"The latter group (women who did not take maternity leave) is significantly more likely to have been promoted by June 30, 2007," the commission said in its report to the Productivity Commission's inquiry into paid maternity leave.

The public service has some of the most competitive family-friendly work provisions in Australia, including 12 weeks paid maternity leave and flexible working hours.

The commission said it had not investigated the cause of the study's findings but said it could be because it was more difficult to find part-time work at senior levels, or because mothers were finding it too difficult to balance home and work to seek more senior positions.

AAP