The Victorian Greens have again been forced to deny allegations of a toxic culture after the latest resignation of a high-profile member who landed a stinging attack as she quit.

Former Spring Street upper house MP Samantha Dunn, who lost her spot at the November state election, unleashed on the Greens' in an online tirade on Thursday, including claims the party is riddled by megalomania.

"The Greens are distracted by populism, self interest, power, ego, narcissism, megalomania, appealing to narrowcast demographics and virtue signalling while exercising that old war strategy of divide and conquer," she wrote.

But the party's Victorian leader Samantha Ratnam denied bullying claims and said she was "surprised" about Ms Dunn's decision to leave.

"I'm really disappointed that Samantha's left the party and that she's chosen to leave the party that way," Ms Ratnam told AAP on Friday.

She found out about Ms Dunn's decision via a social media post but denied the accusations of bullying.

"We're a party that's growing and changing of course there's conflict that arises from time to time," she said.

"I can't speak to Samantha's reasons. She's put a post up about why she might have left the party and that's for her to explain."

The one-term MP was among three of the party's other upper house members, plus Lidia Thorpe from the lower house seat of Northcote, to lose their seats.

Ms Dunn said she was not resigning because she lost her seat, but because "the Greens are too toxic to be part of my life anymore".

The party has been hit by internal disharmony for some time including allegations of bullying and sexual misconduct.

Repeat federal candidate Alex Bhathal quit the party in February, after she was accused of bullying during the Batman by-election.

Upon leaving, Ms Bhathal said she had lost faith in the Greens' governance and felt bullied out of the party. Party leadership at state and federal level rejected her criticism.

Federal Greens MP and co-deputy leader Adam Bandt said the state party was going through a review after the state election and refused to accept accusations of toxicity.

"If there's particular instances that (Ms Dunn) wants to talk about I think many of us would be keen to hear them," he said.

"Alex and Sam are good people and I'm disappointed they have chosen to leave the party."

The party is still reviewing its 2018 election campaign.