Oxidative stress is connected with many human diseases and also contributes to the aging process. There are many studies investigating different antioxidants and their activity. The aim of the M.sc thesis was to determine antioxidative activity of the commercial preparations from the silver fir wood extract and standard antioxidants like: ascorbic acid, resveratrol, epigalolocatechin gallate (EG), butylated hydroxytoluene (BHT), and D-α-tocopherol succinate in two different concentrations (0.05 in 0.1 g dry extract or compound/L) using yeast Saccharomyces cerevisiae as a model organism. The antioxidative activity was determined my measuring intracellular oxidation. It was determined that both commercial wood preparations and EG dissolved in water, decreased the level of yeast intracellular oxidation, where the highest decrease was observed at EG in concentration of 0.1 g/L. Ethanolic extracts of commercial wood preparations at defined concentrations did not decrease the level of oxidation in the cells. Additionally, by measuring culturability we investigated the role of pretreatment of the yeast cells the with water extracts of commercial preparations and EG (0.1 g/L) in the protection of cells against oxidative stress induced with hydrogen peroxide. Culturability of yeasts cells pre-treated with EG was higher compared to the non-treated cells as well as to commercial wood preparations, which did not show any protective role against induced oxidative stress at defined concentration.