Abstract: The activity and isozyme of peroxidase in leaf and root tip of the seedling of two mangrove species, Kandelia candeI and Bruguiera sexangula, cultivated in sand beds irrigated with seawates of different salinity were studied.The results showed that: (1) With increase in salinity, the activity of peroxidase in leaf of K. candel got enhanced in lower salinity (from 0 to 10) and decreased over 15‰ salinity, but the activity in root tip decreased as the salinity increased from 0‰ to 35‰. (2) The activity of peroxidase in leaf of B. sexangula declined with increasing salinity from 5‰ to 35‰, whereas that in root tip increased with salinity from 5‰ to 10‰, and began to decrease over 15. The decreasing trend slowed down in both leaf and root tip in the range of 25--35‰ salinity. (3) The peroxidase activity of Kandelia was less sensitive to salinity than that of Bruguiera. The results showed that peroxidase activity may be used as an indicator of salinity tolerance, ie. Kandelia can grow in higher salinity than Bruguiera. (4) Electrophoresis maps of peroxidase isozyme in two plants on polyacrylamide gel indicated that the main isozyme bands were more stable than the low-class isozyme bands in response to salinity.