The measure of what New Zealand can buy with what it produces fell by 1.3% in the September quarter.
Statistics New Zealand figures show export prices fell 5.2% in the September quarter, more than the 3.9% fall in import prices.
The fall - the sixth in a row - takes the terms of trade index to its lowest level since the December 2005 quarter.
It means fewer imports can be funded by a fixed quantity of exports in the quarter.
Export volumes rose 1% in the quarter, driven by dairy and petroleum products, while import volumes rose 1.9% due to intermediate goods and cars.
The trade-weighted New Zealand dollar rose 7.2% during the quarter.
