The study aims to investigate two sworn charters (charters sealed with oaths), issued on 22th of May 1254, and mutually exchanged between Ragusa (Dubrovnik) and the Principality of Zachlumia. The content of the two documents is considered in parallel with the Bulgarian-Dubrovnik Treaty of 1253. The presented sources reflect a wide palette of political, trade-economic, diplomatic and legal bilateral commitment. As a conclusion, the standpoint is inflicted that these series of agreements put the Serbian kingdom in clear isolation. Against the domain of Stefan Uroš I a broad coalition is formed consisted of several countries and each of these countries accepts to defend the political interests of its partner. The charters are also an indirect evidence for the development of Bulgarian-Hungarian relations during the period under review. On this basis we can point out that the cooperation between Turnovo and Ragusa as reflected in the abovementioned documents is widely applied in the diplomatic contacts established in the European Southeast in the middle of the 13th century. Regarding the development of Bulgarian-Ragusan relations, a conclusion may be made that the bilateral relations are based on the cooperation imposed in the previous decades. Along with that however, the contacts between the Asenid State and the Adriatic Commune undergo further development in terms of an established political agreement between the two countries and an expansion of the existing trade cooperation between them.