The current study was designed to evaluate lipid peroxidation (via malondialdehyde) levels, the superoxide dismutase (SOD) gene expression profile, and SOD enzyme activity in tomato plants (Lycopersicum esculentum L.) subjected to different time periods of cold stress (control, 2, 4, 6, 8, and 10 days). Results revealed that maximum lipid peroxidation occurred in plants exposed to cold stress for 10 days, and SOD enzyme activity gradually increased with increasing exposure to cold stress. The level of mRNA increased within 4 days of cold treatment. After this period, the level tended to decrease and reached a minimum by the eighth day. A complex gene expression profile was determined, which was not statistically significant until the eighth day. At the 10th day of cold treatment, the mRNA level of SOD increased and changes between the 8th and 10th day were found to be statistically significant at the P < 0.05 level. These results suggest that the SOD gene and enzyme play a key role in resistance to cold stress conditions in tomato plants.