The state has been and will always be an "integral and inalienable part of India," foreign ministry spokesperson Arindam Bagchi said on Tuesday.
His comments came after reports said that China had renamed 11 places along a disputed Himalayan border region in the state.
Beijing has not yet commented.
China and India share a disputed 3,440km (2,100 mile) long de facto border - called the Line of Actual Control, or LAC - which is poorly demarcated. The presence of rivers, lakes and snowcaps means the line can shift.
China continues to stake claim on the whole of Arunachal Pradesh, calling it "South Tibet".
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