His colleagues have been handed jail terms of seven and 10 years.
Mr Key told reporters the hallmark of a good and decent society is the respect for the freedom of the press.
“We’re very concerned,” he said.
“In my view, there’s no way that these journalists, on anything I’ve seen, should be being locked up for what was fundamentally doing their job.”
The New Zealand government called on Egyptian authorities to urgently review the prison sentences imposed on the three Al Jazeera journalists.
“The seven-year prison sentences appear to be aimed at silencing critics rather than serving justice,” Foreign Minister Murray McCully said on Tuesday.
“The Egyptian authorities need to understand the international community is watching closely.”