Antioxidant enzyme mechanisms are important for protecting crop productivity against stressful environmental conditions. Therefore, the current study was designed to evaluate lipid peroxidation (via malondialdehyde (MDA)) levels, superoxide dismutase (SOD) gene expression profiles, and SOD enzyme activities in tomato (Lycopersicum esculentum L.) plants subjected to different concentrations (100 and 150 mM) and time periods of NaCl and polyethylene glycol (PEG) stress (3 h, 6 h, 9 h, 12 h, and 48 h). Enhancement of lipid peroxidation in plants may be attributed to the increased accumulation of reactive oxygen species (ROS). Results indicated the antioxidant responses of tomato plants could be reflected as changes in gene transcripts and enzyme activities of SOD, but SOD gene expression patterns and changes in SOD enzyme activity revealed no positive correlation. As a result, stressful conditions led to stress in tomato plants (indicated by increased MDA levels) and triggered the expression levels of the SOD gene. The antioxidative response of tomato plants to PEG stress was found to be more vigorous than the response to NaCl stress. All these results pointed to the importance of SOD for stress defense in tomato. The overexpression and silencing of the SOD gene in tomato plants under NaCl and PEG stresses remain to be identified in further studies.