In forest foci of hemorrhagic fever with renal syndrome (HFRS) of Primorsky Krai Amur and Hokkaido hantaviruses are circulated in the natural host population, i.e. Apodemus рeninsulae and Myodes rufocanus. The indicators of epizootic activity and their threshold values in rodent population dynamics were determined in order to forecast HFRS outbreaks. The material for the research was obtained throughout 2001–2013. The number of trap-nights was 33890. 2737 of A. peninsulae and 1643 of M. rufocanus were investigated. ELISA, RT-PCR, IFA were used for the detection of hantavirus antigen, RNA, antibodies/avidity. The parameters of epizootic activity per 100 TN (N – population, ni – infected rodents, nai – individuals with acute infection) were proposed. The results showed that the active foci of Amur viral infection are located on the slopes of the Sikhote-Alin ridge. The epizootic activity in A. peninsulae populations is characterized by the expressed cyclicity: phase I is rise, phase II is high activity, phase III is recession/low activity. Phases I and II are valid up to a year, whereas phase III is valid within a few years, determining the whole epizootic cycle. In phase I the number of rodents with an acute infection increased from summer to late autumn. In phase II the number of rodents with acute infection was considerable in spring/summer and decreased in autumn more than 3 times. In all phases of the cycle the threshold values were considerably higher for A. peninsulae, than for M. rufocanus, thus showing the former’s epidemiological role in forest ecosystems. HFRS infection rate in phases I/II of the epizootic cycle in A. peninsulae populations had two peaks: during late autumn - winter (≥ 37% of cases) and spring - first half of summer (≥ 55% of cases). The obtained threshold values of Amur hantavirus active circulation in population dynamics of the natural host allows to predict the periods of the increased risk of infection in HFRS forest foci for humans.