Sakai Tadazumi (酒井忠篤, March 22, 1853 – June 6, 1915) was the 11th daimyō of Shōnai Domain during Bakumatsu period Japan.

When his elder brother, the 10th daimyō of Shōnai Sakai Tadatomo died with heir, he was named successor posthumously in 1862 and his position was officially confirmed by the shogunate in 1863.

A couple of months later, he was appointed the commander of the Shinchōgumi and elite paramilitary force of Rōshigumi who were created to provide extra security for the city of Edo.

However, in 1867 growing dissatisfaction over high taxation and a severe crop failure led to widespread rioting and unrest in Shōnai Domain.

Accused by the new government of treason, Tadazumi was forced into retirement in favor of his adopted son, and the domain was reduced to 120,000 koku.