Objective:To observe the extent of brain edema caused by severe cut injury and the protective role of umbilical cord mesenchymal stem cells (UC-MSCs).Methods:A total of 90 female C57L mice were selected and the models of severe cut injury were prepared with surgical blade. According to the random number table, the animals were divided into control group (20 mice), cut group (20 mice), interleukin-6 antibody (IL-6-AB) before cut group (administered IL-6-AB at 18 hours before cut, 15 mice), IL-6-AB after cut group (administered IL-6-AB at 1 hour after cut, 15 mice) and UC-MSCs group (20 mice). The extent of brain edema was detected, the level of IL-6 in brain tissue by ELISA method and the expression of aquaporin-4 (AQP-4) by Western blot assay.Results:Brain water content test showed brain edema in cut group was (81.5±1.8)%, significantly higher than (77.1±2.4)% in control group ( P<0.05). Compared with cut group, brain edema in UC-MSCs group [(76.8±2.4)%] and IL-6-AB before cut group [(76.2±2.9)%] were significantly decreased ( P<0.05), while that in IL-6-AB after cut group [(82.4±1.7)%] was little decreased ( P>0.05). ELISA showed the level of IL-6 in cut group was significantly increased in mouse brain [(16.6±1.3)pg/ml], when compared with control group [(10.3±0.3)pg/ml] ( P<0.01). Compared with cut group, the levels of IL-6 in UC-MSCs group [(10.7±0.6)pg/ml] and IL-6-AB before cut group [(10.1±0.4)pg/ml] were significantly decreased ( P<0.01), while that in IL-6-AB after cut group [(14.9±1.2)pg/ml] was little decreased in mouse brain ( P>0.05). Western blot assay showed that compared with control group (1.0±0.1), the expression of AQP-4 in cut group (2.4±0.5) was significantly increased in mouse brain ( P<0.01). Compared with cut group, the expression of AQP-4 in UC-MSCs group (1.2±0.3) and IL-6-AB before cut group (1.0±0.1) were significantly decreased ( P<0.01), while that in IL-6-AB after cut group (2.3±0.3) was little decreased in mouse brain ( P>0.05). Conclusions:Severe cut injury can increase brain water content and eventually lead to brain edema through upregulating the levels of IL-6 and AQP-4 protein in the brain. Moreover, UC-MSCs effectively prevent the formation of brain edema by inhibiting the above effects.