Viscount Niwa Nagakuni (????, May 22, 1834 – January 15, 1904) was an Edo period Japanese samurai, and the 10th daimyo of Nihonmatsu Domain in the Tohoku region of Japan.
He was the 11th hereditary chieftain of the Niwa clan.
His courtesy title was Saikyo-no-daifu, and his Court rank was Junior Fourth Rank, Lower Grade.