One of the errands given by Nicolae Milescu to his ambassador to China (1673-1676) was to learn the degree of Russian colonization of immense space of Siberia and that of the Far East for the information the tsar’s administration had was incomplete, the data recorded in the „reports from the destination place” sent by the Kazakhs who colonized the new territories were insufficient and even contradictory. All these were done in order to set the future actions of colonization and rising of outcome in Russian treasury through taxing sedentary ethnic or migrating groups. Nicolae Milescu successfully fulfilled the tsar’s order. His information about the Russian colonization of Siberia, namely about the Russian settlements near the banks of the rivers Irtiş, Obi, Enisei, Angara or near those of the Transbaikalia and Dauria, recorded in Jurnalul de călătorie (The Travel Journal), are the vastest and the exactest in the 17th century, further becoming a source for safe information of other travellers and researchers of Siberia and the Far East.