Epizootological role of fleas in the Gorno-Altai natural plague focus (Sailugemsk focus) and numerous data on the flea viability are analyzed and generalized. Information concerning the flea natural infectivity with Yersinia pestis altaica is represented. Ecological peculiarities of some flea species parasitizing the main host, Mongolian pika Ochotona pallasi, and nature of their interrelations with Y. pestis are investigated. It is shown that the flea taxocenosis provides the permanent all year-round circulation of Y. pestis in the Gorno-Altai natural focus. Certain combinations of structural elements of the flea taxocenosis have a dominant significance in determination the circulation process at different phases of the annual epizootic cycle.