People have significantly influenced on Orenburg region steppes by ploughing large parts of it, or by utilising other parts as mowed grasslands, pastures or abandoning crop production on the old abandoned fields. Frequent fires are another serious threat to the biodiversity of the steppes in the region. The main cause of fires is the anthropogenic factor. This problem is relevant not only for managed areas, but also for Protected Areas. The need to study the fire effects on ecosystems in the Orenburg State Nature Reserve (Russia) has appeared for a long time, once it cleared that a special regime of Protected Areas could not always preserve steppes of fire influence due to the steppe's specifics (i.e., significant length of the fire front and a burnt area, high speed of a fire spread under strong wind). At the same time, it is most relevant to conduct environmental studies in the Protected Areas as ecosystems, least managed and disturbed by humans. It is supplemented by excluding of any impacts within these areas and using data of long-term research accumulated over previous years. In 2015-2016, we carried out the post-fire dynamics of the stock of the above-ground phytomass in the site «Burtinskaya Steppe» in the Orenburg State Natural Reserve. The study area is located in the steppe zone of the Pre-Ural region. In August 2014, more than 20 km 2 of the steppe area was on fire. We established six study sites in this area. Each of them included a control (unburnt) and a burnt plots. In each plant community, we conducted the geobotanical surveys and mowing of the above-ground phytomass in spring (May), summer (June), late summer (August), autumn (September). The obtained samples were dried, divided into groups (grasses, forbs, dwarf semi-shrubs) and then weighted. We compared both unburnt and burnt study plots, and found statistically significant differences between them using the Mann-Whitney U-test (α < 0.05) in the total stock of the above-ground phytomass, stock of the dead phytomass, the standing dead phytomass, and litter. In the burnt plant communities, the accumulation peaks of the living grass and forbs phytomass shifted compared to the unburnt plots. During the first two post-fire years, only stock of the living phytomass and its components (grasses, forbs, dwarf semi-shrubs) were restoring. Other components of the above-ground phytomass did not reach the control values. Our data were part of a project for creation a framework to monitor ecosystems in the preserved area after the 2014 fire impact.