To observe the effect of HSM (hypertonic saline/mannitol) on thymic cell apoptosis induced by endotoxin (LPS) in mice, twenty-four mice were divided into three groups (8 mice/each group): 1. Control group, each mouse was intraperitonealy injected with normal saline; 2. LPS group, each mouse was intraperitonealy injected with LPS; 3. LPS + HSM group, each mouse was intraperitonealy injected with HSM before and after injection of LPS. The results showed that the percentage of apoptosis of HSM + LPS group was lower than that of LPS group (P < 0.01); the ladder of nucleosomal DNA fragments by agarose gel eletrophoresis of HSM group was not typical as compared with that of LPS group. It is suggested that HSM might protect the apoptosis of mouse thymic cell induced by LPS and may improve the immune function.