Ionic liquids are organic salts that are in liquid state at temperatures below 100° C. Due to their features such as very low vapour pressure, non-flammability, great dissolving power for a wide range of compounds, their thermal, chemical and electrochemical stability, as well as recycle potential, ionic liquids are extensively studied as a green alternative to traditional organic solvents. However, prior to their use on industrial scale it is crucial to proactively characterize their biodegradation potential and toxicity. Therefore, in this study the impact of two imidazolium ionic liquids (1-butyl-3-methylimidazolium acetate and 1- butyl-3-methylimidazolium tetrafluoroborate) on the germination and growth of barley (Hordeum vulgare) is investigated. The results showed that the selected ionic liquids possess inhibitory effect on the early growth and development of barley, while the inhibitory effect depends on the ionic liquids concentration. Toxic effects of ionic liquids are reflected in reduced amounts of chlorophyll, as well as in increased amount of malondialdehyde (indicator of lipid peroxidation) and H2O2. Furthermore, increased activity of antioxidant enzymes (superoxide dismutase, nonspecific peroxidase, catalase and ascorbate peroxidase) and increased content of non-protein thiols was observed, which indicates their participation in the plant defence mechanism against oxidative stress caused by ionic liquids. However, when seedlings were exposed to higher concentrations of ionic liquids antioxidant system couldn’t effectively remove reactive oxidative particles, leading to lipid peroxidation and damage to the photosynthetic system.