Neiphiu Rio, leader of the Democratic Alliance of Nagaland, was sworn in as chief minister on Thursday.
Governor Shymal Dutta administered the oath of office and secrecy to Rio, 22 Cabinet ministers and six ministers of state at a ceremony at Raj Bhavan in Kohima.
The DAN, a conglomerate of five regional and non-Congress political parties, has 38 legislators in the 60-member assembly.
Among those present in the ceremony were former chief ministers and members of DAN constituents.