Honda Tadamasa (本多 忠政, 1575 – September 6, 1631) was a Japanese daimyō of the early Edo period, who ruled the Kuwana Domain and then the Himeji Domain. He was the son of Honda Tadakatsu.

Honda Tadamasa
Daimyō of Kuwana
In office 1609–1617
Preceded by	Honda Tadakatsu
Succeeded by	Matsudaira Sadakatsu
Lord of Himeji
In office 1617–1631
Preceded by	Ikeda Mitsumasa
Succeeded by	Honda Masatomo
Personal details
Born	1575 Mikawa Province, Japan
Died	September 6, 1631 Edo, Japan
Spouse	Matsudaira Kumahime
Parents	Honda Tadakatsu (father) Achiwa Goemon Gentetsu's daughter (mother)

Tadamasa's first battle was during the Siege of Odawara, in 1590; he also fought at the Battle of Sekigahara in 1600. After his father's retirement in 1609, he succeeded to the Honda family headship, becoming the second generation lord of the Kuwana Domain. Several years later, he took part in the Siege of Osaka, and received the Himeji Domain, with 150,000 koku of revenues, as a reward.

Tadamasa's wife was Kumahime, the daughter of Tokugawa Ieyasu's eldest son Matsudaira Nobuyasu. Their eldest son, Honda Tadatoki (the husband of Tokugawa Hidetada's daughter Senhime), was in line to inherit the Himeji Domain. However, as Tadatoki died in 1626, at age 31, the domain went to his younger brother, Honda Masatomo.

In 1617–1618, Tadamasa and his family inherited Himeji Castle, and he added several buildings to the castle complex, including a special tower for his daughter-in-law, Princess Sen.^[1] In 1628–1629 he rebuilt some of the building at Ichijō-ji that had been destroyed by fire, including the main hall.^[2]