The effect of the phytohormone salicylic acid (SA) on the tolerance of cucumber seedlings (Cucumis sativus L.) to action of the low hardening (12 ºС) and damaging (4 ºС) temperatures was investigated. It was found that the effect of the temperature12 °C on seedlings untreated SA contributes to their hardening, as evidenced by decrease of electrolyte leakage from cotyledons. In contrast, the temperature4 °C had damaging effect on seedlings untreated SA, resulting in an increase of electrolyte leakage. It was also found that there was a decrease of content of the end product of lipid peroxidation (POL) - malondialdehyde (MDA) in leaves and free proline at effect of the temperature12 °C, and at the action of the temperature4 °C – their accumulation. Pretreatment of SA at concentrations of 50 and 100 μM reduced electrolyte leakage from cells of cucumber seedling leaves at the temperature 12 and4 °C. Furthermore, exogenous SA reduced POL leading to a decrease of the level of MDA and also contributed to the accumulation of free proline in cotyledon leaves at the normal temperature (22 °C) and in conditions of the low hardening (12 °C) and damaging (4 °C) temperatures. The data indicate the ability of SA to activate the processes aimed to improving cold tolerance of cucumber plants.