Experiments indicated that the assimilatory branch swelling of Casuarina in coastal areas of Guangdong province was caused by salt injury. Sodium choride and potassium chloride were the main causal agents.The underground parts of Casuarina plants were more tolerant to salt injury than the aerial parts.Chemical analysis of the assimilatory branch samples collected from the coastal plants showed that the contents of chloride ion and sodium ion in the diseased assimilatory branches were 2 times as much as in the healthy ones.Analysis of soil samples taken from the coastal areas showed that the salt injury of Casuarina trees was in relation to the salt content, the amount of organic matter, moisture , and the pH value in the site where the trees had been growing. Experiments also demonstraed the effect of the soil moisture and soil texture on the salt injury of Casuarina,A clonal variation in salt tolerance is apparent. Of 15 clones tested only one was highly tolerant.