Viscount Hoshina Masaari (保科 正益) (March 22, 1833 – January 23, 1888) was a Japanese daimyō of the late Edo period who was the last ruler of the Iino Domain (Kazusa Province; 20,000 koku).

Masaari was born in Edo to the 9th Iino lord, Hoshina Masamoto.

In 1853, Masaari led Iino troops and took part in the defense of Uraga upon the arrival of Commodore Matthew C. Perry and the U.S. Navy's East India Squadron.

As lord of Iino, he held a variety of minor posts in the Tokugawa administration, most notably becoming a wakadoshiyori in the 2nd year of Keiō.

As with many other former daimyo, Masaari became a member of the kazoku as a viscount (shishaku) in the Meiji era.