A new study has found that many Aboriginal children are not enrolling in preschool because of the cost.

The research, conducted by not-for-profit children's services provider SDN, examined the barriers to Aboriginal parents sending their children to preschool.

Report author Debb Mann says preschool should be made free for Aboriginal families.

It would cost the Government $45 million a year, which Ms Mann says is a small investment.

"If the Government's making promises that Aboriginal children will have access, then that has to be facilitated and has to be facilitated quickly," she said.

"We have to move forward very quickly so that kids start on the same playing field."

But the Government has defended the subsidies Aboriginal families receive for their children to attend preschool.

Federal Schools Minister, Peter Garrett, has rejected the suggestion that Aboriginal children are under-represented in preschools around the nation.

Mr Garrett says while he will take the study on board, the Government is investing generously in that area.

"What I'm saying today is that I'm taking note of the report. I want to have a look at it," he said.

"But my level of expectation is that because we're providing such high levels of investment, genuinely high levels, that it will be up to the states to make sure they pick up those issues of need and make sure the kids have got those opportunities for early childhood learning that they need."

New South Wales Community Services Minister, Linda Burney, says the system is already heavily subsidised.

"It costs about $10 a day for an Aboriginal child to go to school and that's really really important," she said.

But the study says that is still too much for some families.