Hoshina Masayuki (保科 正之, June 17, 1611 – February 4, 1673) was a Japanese daimyō of the early Edo period, who was the founder of what became the Matsudaira house of Aizu.

As Masayuki's mother, Oshizu no Kata (1584–1635, later called Jōkō-in) was a servant, Hidetada chose to hide the newborn, then named Komatsu (幸松).

Masayuki was also a patron of Yamazaki Ansai, one of the early figures in Edo-era Japanese Neo-Confucianism, and together with him wrote the famous Aizu House Code, which included a direct injunction regarding the loyalty of the clan to the Shōgun.

Masayuki was a disciple of Yoshikawa Shintō and at his request he was buried according to Shinto rituals on the grounds of Hanitsu Shrine near Lake Inawashiro.

Masayuki's descendants remained enfeoffed at Aizu Domain for the remainder of the Edo period, until they were defeated by the forces of the new Meiji government during the Boshin War.

However, this steadfast loyalty drew the ire of Satsuma and Chōshū, ultimately leading to Aizu becoming one of the most tragic battlefields of the Boshin War.