House prices were up in nine out of 11 regions last month and the national average price also rose.
Real Estate Institute president Howard Morley said the figures showed that the market was in an excellent state of health.
Prices had risen over a five-year period in a "steady and
unbroken" way, despite predictions of a fall, he said.
Prices were up 31 per cent in the two years from May 2003, with Taranaki leading the charge.
House prices there rose 44 per cent between May 2003 and last month, followed by Northland up 35 per cent and Hawkes Bay up 27 per cent.
The institute's latest monthly figures showed the national median rose from $272,000 in April to $275,000 last month.
Prices fell last month only in Nelson/Marlborough and Otago but rose in every other region.
Mr Morley said the residential property market was defying pundits with its May rally - a month he said was not normally noted for increased levels or for price rises.
"Predictions of a reverse in the property market continue to fall on the deaf ears of the house-buying public.
"May is not traditionally a strong month but this latest effort suggests that the long-term trendline for the market is going to remain intact."
Agents sold 9280 properties last month, up on April's 8876.
Mr Morley said this was a remarkably solid effort for this time of the year.
