Abstract: Under 100 mmol/L NaCl stress condition, the effects of sodium nitroprusside (SNP an exogenous nitric oxide donor) on the contents of ion, polyamines and ABA in tomato seedlings were investigiated. The results showed that by the treatment of exogenous NO, plant growth, contents of K+, K+/Na+ ratio were increased and Na+ contents were decreased under NaCl stress and contents of spermine (Spm), spermidine (Spd), total polyamines (PAs), ABA and (Spd+Spm)/Put ratio were remarkably improved, contents of putrescine (Put) were reduced during the whole period of NaCl stress, while Put/PAs values were significantly decreased only during 4～8 d. These results suggested that NO could decrease the damage of NaCl stress in tomato seedlings and elevate the salt tolerance of plants.