Reimar Constantin von Alvensleben (26 August 1809 – 28 March 1892) was a Prussian (and later Imperial German) general.

Born at Eichenbarleben in the Province of Saxony, Alvensleben entered the Prussian Guards from the cadet corps as a second lieutenant on 27 July 1827.

He became first lieutenant on 14 August 1842, captain on 19 September 1848, and major on the Great General Staff on 18 June 1853, whence after seven years he went to the Ministry of War.

He was soon afterwards promoted colonel, and commanded a regiment of Guard infantry up to 1864, when he became a major-general after the Second Schleswig War.

Soon afterwards he succeeded to the command of his division, General Wilhelm Hiller von Gärtringen having fallen in the battle; he was promoted lieutenant-general, and retained this command after the conclusion of peace, receiving in addition the order Pour le Mérite for his services.