Mizoguchi Naoharu (溝口直治, August 23, 1708 – July 7, 1732) was the 6th daimyō of Shibata Domain in Echigo Province, Japan (modern-day Niigata Prefecture).

He was received in formal audience by Shōgun Tokugawa Tsunayoshi in 1694 and became daimyō in 1719 on the death of his father.

Despite this addition income, the domain was unable to free itself from debt due to repeated flood disasters, and was forced to terminate the employment of some low-level samurai and to reduce the stipends of others.

Naoharu was engaged to a daughter of Sakakibara Masakuni of Himeji Domain, but fell ill before the marriage was finalized and the engagement was cancelled.

As he died without heir, the domain quickly adopted Kamenosuke, the son of a hatamoto cadet branch of the clan as heir.