In the late 19th and early 20th centuries, the development of a robust postal and telegraph system, alongside the construction of railways, was a crucial indicator of social modernization. The efficient operation of the Chinese Eastern Railway and its connecting Kaidalovskaya line depended heavily on the organization of communication along the railway. Establishing comprehensive postal and telegraphic communication was also vital for the local population. This study aims to examine the formation of the postal and telegraphic system along the Kaidalovskaya line of the Transbaikal Railway. Due to changes in the administrative affiliation of the Transbaikal region throughout the 20th century, information on this topic is dispersed across various central and regional archives of Russia. These materials are mainly housed in the Russian State Historical Archive, the State Archive of the Republic of Buryatia, the State Archive of the Irkutsk Region, and the State Archive of Zabaykalsky Krai. The authors concluded that creating the postal and telegraph system along the Kaidalovskaya line was a complex and prolonged process. Before the construction of railways, there was no post and telegraph in the administrative centre of the Aginsky Steppe Duma. Although the first post offi ce was opened in Chindant during the construction of the Kaidalovskaya line, the establishment of a fully functional postal and telegraph system in the region was delayed until World War I, primarily due to the insufficient government funding. Despite the authorities’ interest in moder nizing the communication system for the local population and repeated requests from selfgovernment bodies, including the Aginsky Steppe Duma and later the Aginsky Indigenous Volost Administration, postal and telegraph offices along the Kaidalovskaya line were primarily established when and where there was an urgent need for military presence or railway construction.