The estimated number of possums in New Zealand has fallen to about 30 million, down from highs of 70 million in the 1980s.
Landcare Research came up with the figure after it was asked to review the impact of control measures around the country.
Possum control is carried out over an area of about 13 million hectares, which is around half the total area of vegetation in New Zealand.
Landcare scientist Bruce Warburton says the results need to be treated cautiously because the figure is an estimate and possum densities and numbers will vary from area to area.
He says controlling possums helps reduce the spread of bovine TB to cattle and to protect conservation land.