The Green Party has received its largest ever donation, and says it knows nothing about the donor.

The party declared a donation of $283,835 last week from the estate of Elizabeth Riddoch.

The party's general manager Sarah Helm said she believed it was the largest one-off donation in the Greens' 25-year history.

Riddoch, from Nelson, was not a party member and did not appear to have any formal connection to the Greens.

"She wasn't particularly known to the party at all - we haven't been able to determine any link," Helm said.

"She must have just been a quiet, latent supporter of ours."

It is also the largest donation to any political party since 2014, when former Conservative Party leader Colin Craig gave $355,000 to his party.

Helm said most of the Green Party's fundraising was based on small, regular payments.

"We do have a quite comprehensive fundraising programme but a large bequest like this is extremely unusual for us.

"We tend to get a lot of small and medium-sized donations from people who perhaps have some disposable income but aren't the very wealthy in society."

Other large donations to the Greens include a one-off payment of $60,000 by Les Mills International chief executive Philip Mills</a> in 2014.

The Greens raised $408,000 last year, of which $237,000 came from its own MPs under the party's tithing system.

That total was more than Labour, who raised just $279,134.

It was however significantly less than the National Party's fundraising, who declared donations of $1.4 million.