Alvensleben commanded a brigade of guards in the Austro-Prussian War of 1866. At the action of Soor (Burkersdorf) on 28 June, he distinguished himself greatly, and at the Battle of Königgrätz where he led the advanced guard of the Guards Corps, his energy and initiative were still more conspicuous. 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.