To investigate the antioxidant defense system, salt-stress induced changes of antioxidant enzymes were examined in the leaves of mulberry (Morus sp.) of the salt-tolerance cultivar Pei. With increasing salinity up to 150 mM NaCl, the hydrogen peroxide content and the activity of guaiacol-specific peroxidase increased markedly. In addition, the activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase slightly increased at 150 mM NaCl. In contrast, catalase activity with increasing salinity was not correlated with hydrogen peroxide content. The results suggest that under increasing salinity, the primarily prominent peroxidase activity appears to play an active role in scavenging reactive oxygen species in this cultivar, whereas the superoxide dismutase/ ascorbate-glutathione cycle seem to be important consequently.