Count Carl Robert Mannerheim (1 February 1835 – 9 October 1914) was a Finnish aristocrat and businessman.

Mannerheim owned Louhisaari Manor in Askainen, Turku and Pori Province, inherited from his father.

He was forced to declare bankruptcy in 1879, and in 1880 the Louhisaari estate was transferred to his sister Mimmi (Eva Carolina).

Mannerheim thereupon eloped to Paris with his mistress, baroness Sofia Nordenstam (d. 1914), where he had a bohemian lifestyle.

He became active as a resister of the Russification of Finland, and he tried to dissuade his son, who served in the Russian Imperial Army, from joining the Russo-Japanese War.