The neuroinflammatory response induced by microglia plays a vital role in causing secondary brain damage after traumatic brain injury (TBI). Previous studies have found that the improved regulation of activated microglia could reduce neurological damage post-TBI. Phillyrin (Phi) is one of the main active ingredients extracted from the fruits of the medicinal plant Forsythia suspensa (Thunb.) with anti-inflammatory effects. Our study attempted to investigate the effects of phillyrin on microglial activation and neuron damage after TBI. The TBI model was applied to induce brain injury in mice, and neurological scores, brain water content, hematoxylin and eosin staining and Nissl staining were employed to determine the neuroprotective effects of phillyrin. Immunofluorescent staining and western blot analysis were used to detect nuclear factor-kappa B (NF-kappa B) and peroxisome proliferator-activated receptor gamma (PPAR gamma) expression and nuclear translocation, and the inflammation-related proteins and mRNAs were assessed by western blot analysis and quantitative real-time PCR. The results revealed that phillyrin not only inhibited the proinflammatory response induced by activated microglia but also attenuated neurological impairment and brain edema in vivo in a mouse TBI model. Additionally, phillyrin suppressed the phosphorylation of NF-kappa B in microglia after TBI insult. These effects of phillyrin were mostly abolished by the antagonist of PPAR gamma. Our results reveal that phillyrin could prominently inhibit the inflammation of microglia via the PPAR gamma signaling pathway, thus leading to potential neuroprotective treatment after traumatic brain injury.