The thousands of documents cover more than 50 years of New Zealanders' reports of encounters with unidentified flying objects.
Most files suggest natural explanations for the sightings, including meteors and reflections off boat lights.
Among the reports was one from a man who wrote a letter in 1955 to inform authorities he had seen flying saucers, even witnessing one take off.
The files also cover the country's best-known UFO mystery in 1978 in the southern island town of Kaikoura. A cargo plane reported strange lights following it and air traffic controllers detected radar blips that they could not explain.
The documents showed the government carefully took note of such reports, even if some citizens only received a polite thanks for their theories.
New Zealand's Defence Force released the files Wednesday under a freedom of information request.