Twigs of Casuarina were collected from Dongshan and Xiamen Island, China. Crude plasma membrane preparation was obtained from Casuarina twigs by ultra-centrifugation. Sealed plasma membrane vesicles were isolated with aqueous PEG3350-Dextran T500 two phase partitioning. We studied the proline accumulation in twigs and the ATPase activities of plasma membrane of Casurina under different growth conditions. The results showed that free proline content and the PM ATPase activities from unfavorable growth conditions were obviously higher than those from favorable environment. This suggested that Casuarina responded to osmotic stress by increasing osmotic material content and the proton transportation activities of PM ATPase.