We studied the response of cucumber seedlings (Cucumis sativus L.) of the hybrid F1 Zozulya to 3‑day exposure to low positive temperatures of different intensities (12 °C and 4 °C). It was found that at initial phases of the impact low hardening (12 °C) and damaging (4 °C) temperatures inhibit the process of accumulation of cotyledons’ wet and dry biomass, promote the activity of the antioxidant enzyme superoxide dismutase (SOD), enlarge the content of free proline and the final product of lipid peroxidation (LPO) – malondialdehyde (MDA). Extended 3‑day exposure to the hardening 12 °С temperature re-launched growth processes with further increase of SOD activity and the level of free proline in leaves, thus promoting the cold tolerance of cucumber seedlings. In contrast, exposure to the damaging 4 °C temperature for 1–3 days caused irreversible inhibition of the accumulation of cotyledons’ wet and dry biomass, a significant increase of MDA and free proline, a decrease of SOD activity, and a decline of cold tolerance, eventually leading to damage and death of the seedlings. It was concluded based on these data that the character and dynamics of physiological and biochemical parameters in the cucumber plants exposed to low hardening and damaging temperatures can vary both quantitatively and qualitatively depending on the intensity and duration of the impact.