The topic of this thesis is the military expedition that Roman emperor Julian undertook against Sassanid Persia in 363 AD. The paper begins with an analysis of historiographical sources that are relevant for Julian's Persian campaign. The following chapters present the internal state of the Roman Empire and the structure of the Roman army in the 4th century, as well as Roman military equipment. An integral part of this work is also a description of the structure of the Sasanian state, military equipment and common war tactics. The strategic and ideological reasons for the Sassanid military pressure towards the west are also described. These are factors that are particularly important for understanding the causes of the frequent wars between the Roman Empire and Sassanid Persia, including Julian's campaign. The course of this conflict before Julian's accession to power is also presented in this thesis, while a separate chapter presents emperor Julian's biography, which is important for determination of Julian's personal motives for starting the campaign. The course of the campaign has been reconstructed by the usage of scientific literature and written sources, of which Ammianus Marcellinus and Zosimus particularily stand out. All significant conflicts fought during the campaign are described, and Julian's reasons for making certain decisions that affected the outcome of the entire campaign are explained. The thesis ends with a description of the consequences of the campaign in the area of the Middle East and the Roman Empire as a whole.