At the start of this war, which mostly took place in Eastern Bohemia (Czech Republic), Gablenz was considered to be one of the foremost Austrian generals. During this war Gablenz commanded the X Corps in FZM Benedek’s Northern Army. Although victorious against Bonin's I Corps at Trautenau (Trutnov, 27 June 1866) in the only Austrian victory against the Prussians, Glabenz's position became untenable due to the Austrian loss at Náchod and the Prussian Guard Corps' advance towards Eipel (Upice), and he was ordered to retreat towards Prausnitz to block the Prussian Guards. The next day at Burkersdorf, Gablenz managed to extricate his corps though with heavy casualties. After reuniting with the main army Gablenz and X Corps fought at Königgrätz (Hradec Králové).