The article discusses the role of leading Russian diplomats in the development of Sino-Russian relations at the turn of the 20th century. It is based on rare archival documents and memoirs written by contemporaries of the described events. The article presents and analyzes the assessments given to their activities in the publications of Russian, Chinese and Western historians. The authors focus their attention on the activities of two ambassadors to China: Arthur Cassini and Pavel Lessar, who headed Russian diplomatic mission in the Qing Empire during
difficult periods of China’s history and the conditions of complicated international situation in East Asia. The first of them served there at the time of the Sino-Japanese War, while the second — in the period between the Boxer Rebellion and the Russo-Japanese War. The clash of interests of the great powers in China at the turn of the 20th century predetermined the complex tasks faced by Russian diplomacy. The analysis of the activities of the Russian Envoys to China, Cassini and Lessar, demonstrates the significant role of career diplomats at that time and proves that Russian diplomats of the late 19th — early 20th centuries were well prepared and, even without special education in oriental studies, but having experience of diplomatic work in different countries and being able to analyze the contemporary international situation, could make correct decisions in hard situations, promoting the prestige of Russia and solving the intricate problems of foreign policy.