Objective To observe the protective effects of melatonin against spinal cord injury from seawater immersion in rabbits.Methods The 120 mature and health New Zealand White rabbits,weight range from 2.6 to 2.9kg,were randomly divided into four groups (30 each):control group,ethanol group,melatonin group (100mg/kg),methylPrednisolone group (30mg/kg).The rabbit model of spinal cord injury were built by modified Allen's method taking the 10th thoracic vertebra as a center,seawater immersion for 60 minutes,and then by grouping to give the appropriate treatment.After each group was given the corresponding treatment,six rabbits in each group were randomly selected at 1,6,12,24 and 48 hours five different time points.The neurological function scores of the rabbits were evaluated by Tarlov method,the spinal cord ofT9 to T.which were obtained from all the groups were used for further study,including immunohistochemical detection of apoptosis proteins:Bax,Bcl-2,neurofilament protein 200 (NF200) and in situ end labeling (TUNEL) method to detect spinal neuronal cell apoptosis.Results Within each observation time point,the Tarlov score was higher in melatonin group and methylprednisolone group compared with control group and ethanol group (P＜0.05),there was no significant difference between melatonin group and methylprednisolone group (P＞0.05).The expressions of Bcl-2 and NF200 were significantly higher in melatonin group and methylprednisolone group compared with control group and ethanol group,while Bax expression was significantly lower (P＜0.05).There were no significant difference between melatonin group and methylprednisolone group in the expression of three proteins (P＞0.05).The TUNEL-positive apoptotic cells were fewer in melatonin group and methylprednisolone group compared with control group and ethanol group (P＜0.05),and there was no significant difference between melatonin group and methylprednisolone group (P＞0.05).Conclusion Melatonin has protective effect against spinal cord injury from seawater immersion in rabbits,no difference in efficacy exists compare with methylprednisolone.