This study formulates a list of constitutional principles of the Kingdom of Sicily under Frederick II Hohenstaufen based on the provisions of the Constitutiones Regni Siciliae from 1231. The aim is to systematize the main assumptions of the emperor’s legislation, which sought to create a specific constitutional system, sometimes referred to as a medieval absolutist monarchy. The reason for choosing the Liber Augustalis for the basis of this analysis was its adoption at the peak of Frederick II’s rule. It is therefore safe to assume that it best reflects the main tenets of the emperor’s political and legal doctrine. The research methodology included an analysis of the legal text and a comparison of the results with the findings of historians regarding Frederick II’s actions in other areas. The resulting catalogue consists of four basic principles: 1) the sacralization of power, 2) the sovereignty of the monarch’s power, 3) the rule of law, and 4) the concentration of power. The article provides a new perspective on the Constitutiones Regni Siciliae not only as a legal text, but also a historical source and political manifesto.