Drought stress is one of the main stresses that inhibit the growth of plants due to mainly disturbance of the balance between production of ROS and antioxidant defense mechanism and causing oxidative stress. Sodium nitroprusside (SNP) commonly was used as nitric oxide (NO) donor in plants. In this study, the effect of different concentrations of SNP on alleviation of oxidative stress induced by drought was investigated. Results of the measurements of lipid peroxidation and photosynthetic pigments content showed that low concentration of SNP could protect plants against oxidative stress because under SNP treatment, lipid peroxidation decreased and pigment loss was ameliorated. In this study, the relationship between this defense mechanisms and activity of antioxidant enzymes was investigated. Results showed that drought stress increased the activity of ascorbate peroxidase, guaiacol peroxidase and catalase. Concentration of 100 and 200 µM of SNP increased the activity of APX had no effect on activity of GPX and decreased the activity of CAT in plant under drought stress. In plants which were under drought stress the activity of PAL also increased but the concentration of 100 and 200 mM of SNP had no effect on activity of these enzymes under drought stress. The concentration of 500 mM of SNP decreased the activity of PAL in drought stressed plants. Drought stress and 100 mM SNP treatments had no significant effects on phenol content and 100 and 200 mM of SNP decreased the amount of these compounds under drought stress. In conclusion, in tomato plants, pretreatment with concentration of 100 mM of SNP or below could protect the plants under drought stress, probably through the contracts with ROS and or induction of anti-oxidative enzymes.