Flavius Claudius Julianus, often referred to as “Julian the Apostate,” ruled the Roman Empire from early 360 AD until his death in battle on June 26th, 363 AD. Despite his brief reign, Julian undertook sig­nificant reforms targeting various aspects of public life, including the administration and provincial governance. This paper focuses on his administrative activities in Illyricum, where he resided in 361 AD while campaigning against Constantius II. While facing immediate tactical concerns during his campaign, Julian reportedly engaged in imperial administrative duties within Illyricum, as documented by historian Ammianus Marcellinus and panegyrist Claudius Mamertinus. This research delves into Ammianus’ account to analyze Julian’s adminis­trative acts in Illyricum and subsequently across the Roman Empire. Flavij Klavdij Julijan, pogosto imenovan »Julijan Odpadnik«, je vladal rimskemu cesarstvu od začetka leta 360 do svoje smrti v bitki 26. junija leta 363. Kljub kratki vladavini je Julijan izpeljal vrsto pomembnih reform, usmerjenih v različne vidike javnega življenja, vključno z upravljanjem provinc. Članek se osredotoča na njegove upravne dejavnosti v Iliriku, kjer je leta 361 po Kr. bival med kampanjo proti Konstanciju II. Med­tem ko se je Julijan med kampanjo soočal z neposrednimi taktičnimi težavami, je v Iliriku opravljal cesarske upravne naloge, kot poročata zgodovinar Amijan Marcelin in panegirist Klavdij Mamertin. Raziskava se osredotoči na Amijanovo poročilo in analizira Julijanove upravne dejavnosti v Iliriku ter v celotnem rimskem cesarstvu.