Objective : To investigate the effect and mechanism of exosome ( Exo) transported miR⁃223 on brain tissue injury and microglial activation in rats with traumatic brain injury ( TBI) . Methods : The miR⁃NC plasmid and miR⁃223 mimic plasmid were transfected into HEK293 cells by liposome method , and the expression level of miR⁃223 in the cells was determined by quantitative real⁃time PCR . Exo was extracted from transfected HEK293 cells and identified by transmission electron microscopy , nanoparticle tracking analysis and Western blot , the expression level of miR⁃223 in Exo was determined by quantitative real⁃time PCR . Forty SD rats were randomly divided into sham group , model group , NC⁃Exo group and miR⁃223 ⁃Exo group , with 10 rats in each group , TBI model was prepared by modified Feeney free fall method in all groups except sham group , rats in NC⁃Exo group and miR⁃223 ⁃Exo group were injected with cell⁃derived Exo transfected with miR⁃NC plasmid and cell⁃derived Exo transfected with miR⁃223 mimic plasmid via tail vein , respectively . Two weeks later , hematoxylin⁃eosin (HE) staining was used to observe the pathological changes of brain tissue in each group , Nissl staining was used to detect the changes and distribution of Nissl bodies in each group , enzyme⁃linked immunosorbent assay (ELISA) was used to measure the serum levels of tumor necrosis factor⁃α (TNF⁃α ) , interleukin⁃1β (IL⁃1β) and interleukin⁃6(IL⁃6) , immunofluorescence double staining was used to observe the expression of nod⁃like receptor family pyrin domain containing 3(NLRP3) and ionized calcium binding adaptor molecule 1 (Iba⁃1) , Western blot was used to detect the protein expression of NLRP3 , apoptosis⁃associated speck⁃like protein containing( ASC) and Caspase⁃1 . Results: After transfection , compared with control group and miR⁃NC group , the relative expression of miR⁃223 in miR⁃223 group significantly increased (P < 0. 05) . The isolated particles had typical Exo morphology , the peak particle size was about 120 nm , the Exo marker proteins CD9 , CD63 and CD81 were significantly overexpressed , and the relative expression of miR⁃223 significantly non of brain tissue in the miR⁃223 ⁃Exo group was improved , the morphology and number of Nissl bodies were re⁃increased (P < 0. 05) . Compared with the model group , the damage phenome stored , the levels of TNF⁃α , IL⁃1β and IL⁃6 in serum decreased ( P < 0. 05) , the intensity of NLRP3 and Iba⁃1 fluorescence staining in brain tissue decreased (P < 0. 05) , the relative protein expressions of NLRP3 , ASC and Caspase⁃1 in brain tissue were down⁃regulated (P < 0. 05) . Conclusion Exo operation of miR⁃223 can significant ly improve brain tissue injury and inhibit microglial activation in TBI rats , which may be related to the inhibition of NLRP3 .