Objective To observe the success rate and rewarming curve of different water bath rewarming in rats with severe seawater immersed hypothermia. Methods A total of 490 male SD rats were intraperitoneally implanted with temperature recorder before experiment, were randomly divided into immersion group (n=450) and control group (n=40). In immersion group 100 rats were immersed in (15.0±0.2)℃ seawater for 2 h, 150 rats for 5 h, and 200 rats for 10 h. The survival rats of each group were randomly divided into five subgroups and given different rewarming treatments:passive rewarming (passive rewarming subgroup), 37℃ hot water bath rewarming for 0.5 h (37℃ active rewarming 0.5 h subgroup), 37℃ hot water bath rewarming for 1 h (37℃ active rewarming 1 h subgroup), 42℃ hot water bath rewarming for 0.5 h (42℃ active rewarming 0.5 h subgroup), 42℃ hot water bath rewarming for 1 h (42℃ active rewarming 1 h subgroup). The rats in the control group were without seawater immersion, and were randomized into four subgroups as above. The success rate of rewarming was calculated in each group. The serum levels of creatine kinase isoenzyme (CK-MB), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were determined in the survival rats after rewarming for 20 h. Dynamic intraperitoneal temperature was recorded at the end of the experiment, and then the passive rewarming velocity, delay afterdrop effect of hot water bath rewarming were calculated. Results With the prolongation of immersing time, the survival rate of rats was significantly decreased in the immersion group (P<0.05). The rewarming success rates were significantly decreased in both the passive and active rewarming groups (both P<0.05). The rewarming success rate in the 37℃ active rewarming 1 h subgroup was greater than or equal to other active rewarming subgroups and the passive rewarming subgroup. All rats in the control group survived after hot water bath. Compared with the control group, the serum levels of CK-MB, ALT and LDH were significantly increased in the surviving rats of the active rewarming subgroups with the prolongation of immersion time (P<0.05). At the same immersing time, the levels of CK-MB, ALT and LDH were significantly lower in the 37℃ active rewarming 1 h subgroup than those in the other active rewarming subgroups (P<0.05 for some results), and were lower than those in the passive rewarming subgroup (P<0.05 for some results). Rewarming curve showed that the rewarming velocity of the passive rewarming subgroup significantly decreased with the prolongation of immersing time (P<0.05), and the rewarming velocity of the dead rats was significantly lower than that of the surviving rats (P<0.05). Delayed afterdrop effect was found in abdominal temperature of hot water rewarming rats, and the greater the effect was, the higher the mortality rate was. The delayed afterdrop effect of 37℃ hot water bath was not obvious in the control group, but it was significantly obvious in 42℃ hot water bath subgroups (P<0.05). Conclusion The success rate of proper hot water bath rewarming is greater than that of passive rewarming in the treatment of severe seawater immersed hypothermia. Hot water bath can be used as a rewarming option in emergency situations, while improper rewarming conditions can decrease the treatment success rate, which may be related to the delayed afterdrop effect.