The West Australian Parliament has formally apologised to the unmarried women who were pressured to adopt out their babies between the 1940s and 1980s.

More than 100 people packed the public gallery to witness the apology and applauded the Premier when he finished his speech.

Colin Barnett acknowledged the policies of the day were unsupportive of pregnant, unmarried women and offered this apology on behalf of Parliament.

"Now apologises to the mothers, the children and the families who were adversely affected by these past adoption practices and express my sympathy to those individuals who were not best served by the policy of those times," he said.

The apology received bipartisan support in Parliament.

The Opposition Leader Eric Ripper says WA is the first state in Australia to formally say sorry for past adoption practices.

"What we do today is unequivically and sincerely apologise to the mothers for fundamentally flawed government policies that meant your babies were taken from you," he said.

"I'm sorry, the state Labor parliamentary party is sorry."

Several female MPs have told State Parliament that they have been personally affected by the forced adoptions of last century.

The Liberal MP, Liza Harvey, says her mother was forced to give up her baby.

"After a long, traumatic and difficult birth she had my sister taken from her to be adopted out," she said.

Ms Harvey says her sister was returned to her mother five weeks later, when she married the father.

The Member for Fremantle, Adele Carles, says her 53 year old mother only recently discovered she was adopted out.

"She had been removed from her teenage birth mother in New Zealand in the 1940s," she said.

Sue MacDonald was 16 when she had her baby taken from her in 1968.

She says she has been waiting a long time for this day.

"Finally women are going to be acknowledged for the pain and suffering that we endured back then, hopefully it will help our children to understand that they weren't given away, they weren't abandoned or given away and I think that this can only set people free," she said.

At the time it was revealed that an apology would be made, several affected women came forward.