Objective To investigate the protective effect of microRNA-181b (miR-181b) on aged rats with sepsis-induced hippocampus injury in vivo. Methods Seventy-five male healthy old Sprague-Dawley (SD) rats were randomly divided into five groups (n = 15) using a random number table: sham operation group (Sham group), sepsis group [cecal ligation and puncture (CLP) group], miR-181b Agomir+CLP group (Ag+CLP group), miR-181b Antagomir+CLP group (An+CLP group) and normal saline (NS) control group (NS+CLP group). Rats sepsis model was reproduced by CLP, and in Sham group, the cecum of rats was separated only after abdominal operation without ligation or perforation. The rats in Ag+CLP group were given miR-181b Agomir 10 μL via lateral ventricle at 24 hours before CLP, the rats in An+CLP group were given 10 μL miR-181b Antagomir, and those in NS+CLP group were given 10 μL NS. At 6, 12, 24 hours after CLP, 5 rats of each group were sacrificed randomly, and hippocampus were harvested. The expression of miR-181b in hippocampus was determined by real-time fluorescence quantitative reverse transcription-polymerase chain reaction (RT-qPCR). The expression of nuclear factor-κB p65 (NF-κB p65) was determined by Western Blot. The contents of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) were determined by enzyme-linked immunosorbent assay (ELISA). Results Compared with Sham group, the expression of miR-181b in hippocampus of CLP group was significantly decreased at 6 hours after CLP (2-ΔΔCT: 0.70±0.12 vs. 0.98±0.06, P < 0.05), and the expressions of NF-κB p65, IL-1β and TNF-α were significantly increased [NF-κB p65/Histone H3:0.30±0.03 vs. 0.07±0.01, IL-1β (ng/L): 120.39±8.02 vs. 50.55±11.12, TNF-α (ng/L): 59.48±4.60 vs. 40.31±3.96, all P < 0.05], this trend was continued till 24 hours, and these results indicated that there was obvious inflammation in hippocampus of sepsis rats. There was no statistical difference in the expression of miR-181b, NF-κB p65, IL-1β or TNF-α in hippocampus between NS+CLP group and CLP group, which indicated that injection of NS into the rat lateral ventricle, had not aggravated the damage degree of hippocampus. Compared with CLP group, the expression of miR-181b in hippocampus of Ag+CLP group was significantly increased at 6 hours after CLP (2-ΔΔCT: 1.87±0.25 vs. 0.70±0.12, P < 0.05), and the expressions of NF-κB p65, IL-1β and TNF-α were significantly lowered [NF-κB p65/Histone H3:0.16±0.03 vs. 0.30±0.03, IL-1β (ng/L): 73.76±8.17 vs. 120.39±8.02, TNF-α (ng/L): 49.52±4.77 vs. 59.48±4.60, all P < 0.05]. There was no statistical difference in the expression of miR-181b in hippocampus between An+CLP group and CLP group (2-ΔΔCT: 0.80±0.08 vs. 0.70±0.12 at 6 hours, 0.48±0.03 vs. 0.46±0.05 at 12 hours, 0.61±0.09 vs. 0.63±0.07 at 24 hours, all P > 0.05), but the expressions of NF-κB p65, IL-1β and TNF-α in hippocampus at 6 hours after CLP of An+CLP group were significantly higher than those of CLP group [NF-κB p65/Histone H3: 0.44±0.02 vs. 0.30±0.03, IL-1β (ng/L): 134.21±5.78 vs. 120.39±8.02, TNF-α (ng/L): 67.62±5.86 vs. 59.48±4.60, all P < 0.05], this trend was continued till 24 hours after CLP. The above results showed that overexpression of miR-181b might attenuate the inflammation of hippocampus through down-regulation of NF-κB, IL-1β and TNF-α. Conclusions The expression of hippocampal miR-181b was significantly decreased in septic rats. Up-regulation of miR-181b could inhibit the activation of NF-κB signal pathway and the release of the inflammatory cytokine IL-1β and TNF-α stimulated by sepsis, and alleviate the inflammatory reaction and hippocampus injury in rat with sepsis.