From October, a regular New Zealand Post stamp will cost 60 cents - a 10 cent rise on the current cost.
That rise will also include the increase in GST from October.
New Zealand Post CEO Peter Fenton said rising costs and declining mail volumes were hitting the company hard.
He said in the past five years, the number of letters and parcels sent had dropped by more than 100 million to 887 million.
The latest rise comes three years after the price of a stamp increased from 45 to 50 cents.