New information collected from the Census shows a drop in the number of Te Reo speakers.
Just over one in five Maori can now hold a conversation in their native tongue.
That's a decrease of 4.8% since the last official count in 2006.
The ability to speak Te Reo has fallen across all age ranges, except among the over 65s where it is up 11%.
There's also been a slide in the number of Maori who can speak more than one language, dropping 4.9% to 125,388 people.
Meanwhile, the Maori population has climbed 5.9% to 598,605.
The rise is faster than the increase in the overall population of New Zealand, which has grown by 5.3 % or 214,101 people.
Statistics New Zealand says the biggest surprise in the information is the number of Maori achieving formal qualifications at university.
The proportion of Maori with a bachelor's degree has increased by 56.4% to 36,072.
Hindi is now the fourth most common language in New Zealand, after English, Maori and Samoan.
