An outgoing WA Liberal MP has called for the party to adopt gender-based targets after the party's landslide defeat in the state election left only three female Liberal MPs in Parliament.

Last month's election ended many Liberal MPs' careers and left a huge dent in the number of Liberal women in Parliament.

From May, just three of the party's 22 MPs will be women — Libby Mettam, Donna Faragher and the party's deputy leader Liza Harvey.

Liberal MP Robyn McSweeney lost her seat in the Legislative Council after 16 years in politics.

"We need targets and we need women of all diversity in Parliament," she said.

"It's not good enough to just have three Liberal women."

Ms McSweeney said the party needed to set targets, much like WA Labor's quota system.

"If we don't set targets with teeth, targets that can be backed up, then we are going to be left behind," she said.

"We are going to be seen as a boys' club — I believe that we should have 40 per cent targets but those targets need to be enforceable."

Some female MPs remain unconvinced by gender quotas

The former minister for women's interests said there needed to be more effective mentoring to encourage women to enter into politics and, more importantly, stay.

"We say that a woman can get there by her own merit but when you're up against a lot of men, maybe a woman doesn't have much confidence," Ms McSweeney said.

"Maybe a comment or two can put a woman down — they don't have the confidence to keep going."

New Liberal leader Mike Nahan does not support gender quotas. ( ABC News: Andrew O'Connor )

But even other women within the party who want to attract more women into politics do not agree with a quota.

"By a quota system and a firm quota, you never know whether you're the best person for the job," Liberal MP Liz Behjat said.

"It needs to be the best person for the job that gets there."

New WA Liberal leader Mike Nahan does not support gender quotas but does want to open the preselection process to all party members.

"I'm confident that we will broaden the selection base, broaden the range of candidates, and broaden grassroots support for the Liberal Party," he said.