Objective 　To evaluate the effects of regional seawater immersion on the pain behavior and its secondary neuropathological change in the rats model of skin/muscle incision and retraction (SMIR). Methods 　Forty-eight male SD rats were randomly assigned into 3 groups (16 each): the model control group (only to set up SMIR model, Group MC), normal saline immersion group (to set up SMIR model and the incision immersed with normal saline, Group NS), seawater immersion group (to set up SMIR model and the incision immersed with seawater, Group SW). Mechanical paw withdrawal threshold (MWT) was measured 1d before and 1d, 3d, 5d, 7d, 14d, 21d and 28d after operation, respectively. At 3d and 28d after the operation, 8 rats were randomly selected from each group, ipsilateral saphenous nerves were taken from 4 rats for HE staining, and dorsal root ganglion of ipsilateral L3/L4 were taken from another 4 rats for ultrastructural observation by electron microscopy. Results 　Compared with the other two groups, MWT values in Group SW significantly reduced at every observation time and remained significantly lower than the basic level at 28d. There were no differences in MWT values between Group MC and Group NS, and the MWT values of the two groups at 28d were comparable with preoperative basic level. The HE staining of Group SW showed saphenous nerves were injured, while of Group MC and Group NS were normal. A large number of vacuolar mitochondrion and autophagosomes were observed in dorsal root ganglion of Group SW and few swelling mitochondrion was found in the other two groups. Conclusions 　Regional seawater immersion can aggravate the pain evoked by SMIR and may result in chronic pain. Peripheral nerve injury, ultrastructure changes of dorsal root ganglion neurons in rats caused by regional seawater immersion may be involved in the mechanism of the change of pain behavior. DOI: 10.11855/j.issn.0577-7402.2016.07.07