NDPP leader Neiphiu Rio was on Thursday sworn in as Nagaland chief minister by Governor P B Acharya at a public function here.
This is Rio's fourth time as the chief minister of the Northeastern state.
Rio is heading the 'People's Democratic Alliance' government in partnership with the BJP in the state.
BJP's Y Patton was administered the oath as the deputy chief minister by the governor.
Ten other ministers were also administered the oath of office.
The 10 included five from the BJP, three from the Nationalist Democratic Progresstive Party (NDPP), an independent and a JD(U) MLA.
Defence Minister Nirmala Sitharaman, Union minister Kiren Rijiju, BJP president Amit Shah and the party general secretary Ram Madhav were present at the swearing-in ceremony.
The outgoing chief minister T R Zeliang was also present at the function.
The chief ministers of Assam, Arunachal Pradesh, Manipur and Meghalaya also attended Rio's swearing-in.
Rio had staked claim to form the government on March 4 with the support of 32 legislators in the 60-member House - 18 MLAs of NDPP, 12 of the BJP, one of the JD(U) and an independent MLA.