Hypoxic-ischemic　brain　damage　(HIBD)　is　a　leading　cause　of　infant　mortality　and　neurological　disabilities　in　children.　Recent　evidence　indicates　that　gut　microbiota　significantly　contributes　to　the　development　of　inflammation　and　cognitive　impairments　following　brain　injury.　However,　the　mechanisms　by　which　gut　microbiota　influence　inflammation　and　cognitive　function　in　the　neonates　after　HIBD　are　not　well　understood.　This　study　established　a　neonatal　rat　model　of　HIBD　by　the　classic　Rice-Vannucci　technique　to　investigate　gut　dysbiosis　following　hypoxic-ischemic　(HI)　insult　and　to　elucidate　the　causal　relationship　between　gut　dysbiosis　and　cognitive　impairments.　Our　results　demonstrated　that　HI　insult　resulted　in　significant　gut　microbial　dysbiosis,　characterized　by　an　expansion　of　Enterobacteriaceae.　This　dysbiosis　was　associated　with　intestinal　barrier　damage,　lipopolysaccharides　(LPS)　leakage,　and　systemic　inflammation.　Conversely,　administration　of　aminoguanidine　(AG)　to　inhibit　Enterobacteriaceae　overgrowth　restored　intestinal　barrier　integrity　and　reduced　systemic　inflammation.　Importantly,　AG　treatment　effectively　suppressed　microglial　activation,　neuronal　damage,　and　cognitive　impairments　in　the　neonatal　rats　subjected　to　HI　insult.　Additionally,　RNA　sequencing　analysis　revealed　that　differentially　expressed　genes　in　both　colonic　and　hippocampal　tissues　were　primarily　associated　with　inflammation　and　neuronal　apoptosis　after　HI　insult.　Further　mechanistic　exploration　revealed　that　AG　treatment　mitigated　intestinal　LPS　leakage,　thereby　reducing　the　activation　of　the　TLR4/MyD88/NF-kappa　B　signaling　pathway　and　production　of　the　downstream　inflammatory　cytokines　in　both　the　colon　and　hippocampus.　Notably,　fecal　microbiota　transplantation　(FMT)　from　the　HIBD　rats　to　the　antibiotic　cocktail-treated　recipient　rats　resulted　in　microglial　activation,　neuronal　damage,　and　cognitive　impairments　in　the　recipients.　However,　these　adverse　effects　were　effectively　mitigated　in　the　recipient　rats　that　received　FMT　from　the　AG-treated　donors,　as　well　as　in　those　undergoing　hippocampal　TLR4　knockdown.　In　conclusion,　our　findings　indicate　that　LPS　derived　from　gut　Enterobacteriaceae　overgrowth　plays　a　critical　role　in　the　TLR4-mediated　inflammatory　signaling,　providing　a　novel　microbiota-based　therapeutic　approach　for　cognitive　impairments　following　neonatal　HIBD.