Celja-Austria was, also Celje-Habsburg war, took place in the first half of 15th century on wider Slovenian area and Istria. The war was between Celje Counts and Habsburgs and allies.

The Causes for war were tendencies to increase the estate holdings in this area. There was a dispute between Frederick II. of Celje and Krško bishop Johann Scholdermann due to an estate in the vicinity of Celje. Due to that noble families in Slovenia divided into two camps: Celje and Austrian. These camps were formed on the basis of existing contracts, disputes or agreements.

In the first part of the war, Celje took over the Habsburgs territories in Posavje and Lower Carniola, as well as on Austrian Styrian. After that, in year 1440, the two parties signed a peace treaty in Hainburg. This truce lasted from August 23rd until April 1st 1442. In time of truce Krško bishop had given to Celje as war recompense the following castles: Rogatec, Podčetrtek, Mokronog, Pilštanj and Bizeljsko. That year the Celje-Hungarian war started, but Celje army defeated Hungarian on March 1st 1441 at Samobor pod Gorjanci.

After the end of the peace treaty both Celje and Habsburg gathered new forces, and it came to another war, mostly in the area of Carniola. Ljubljana and Novo mesto were under Austrian control, both cities were unsuccessfully occupied by Celje. They represented the last major obstacle for authorities of Celje between Drava and Istria. On August 16th 1443 in Wien Novo mesto they again signed a peace treaty, as well as mutually hereditary contract.

Between Celja-Austrian war, Celje managed to increase its estates, but they did not succeed strategically connect this estates so they would work as a whole. Because they did not succeed to take Ljubljana and Novo mesto, the belt Klagenfurt-Ljubljana-Novo mesto remained in possession of Habsburgs. These estates, after extinction of Celje counts, were taken over by Habsburgs, at the same time they also gained back the estates, which they lost in the war.

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