The measure of what New Zealand can buy with what it produces, has fallen by 9% - the largest amount in more than half a century.
Statistics New Zealand figures show export prices fell 11.6% in the three months to June, much more than a 2.9% fall in import prices.
The terms of trade index is now at its lowest level since the September 2006 quarter.
UBS senior economist Robin Clements says the latest quarterly fall is much larger than predicted.
Overall terms of trade fell 13% in the year to June - the largest fall since 1980.