Theorem of climate change impact on forest vegetation zones of Krivánska Fatra Mts. The aim of this paper is to analyze change of the ecological conditions of forest vegetation zones of Krivánska Fatra Mts and evaluate the response of vegetation to climate change for the period 1974 – 2015. Phytocenological relevés in the vegetation zones of Krivánska Fatra Mts were realized in 1974 and re-entries were realized in the permanent study / stationary areas of the national nature reserves Rozsutec and Chleb between 2014 and 2016. Impact of climate change on vegetation in the past 40 years was assessed using the Ellenberg ecological indices and diversity indexes of the assessed communities. The values of ecological indices computed from 99 phytosociological records done in 1974 in the forest vegetation zones of Krivánska Fatra Mts were compared with nation-wide values of the indices in the same forest vegetation zones. The differences of average values of the ecological indices between 1974 and 2015 were not statistically significant. Also the tree species composition in the repeated phytocenological entries realized the past 45 years, revealed no significant changes. To summarize, ecological analyzes of forest phytocenoses in the forest vegetation zones of Krivánska Fatra Mts did not confirm the theorem of recent climate change impact on the forest vegetation zones of these mountains. This can be explained by the strong buffer effect of the forest cover, esp. by maintaining relatively stable forest microclimate (light, temperature, moisture) under the forest canopy. However, the species composition of forest ecosystems has been partly influenced by acidification and eutrophication of the environment in the second half of the 20th century.