〔Abstract〕 Objective Mendelian randomization analysis was used to explore the causal relationship ofT.gondiiinfection and the cyst distribution and inflammation in brain tissue by immunohistochemistry. Methods Genome-wide association analysis data ofT.gondiiinfection and encephalitis were obtained, single nucleotide polymorphisms(SNPs) were selected, Mendelian randomization analysis was conducted by inverse variance weighting, and the causal relationship betweenT.gondiiinfection and encephalitis was evaluated byORvalue and 95%CI. Quality control was carried out by using heterogeneity test, horizontal multi-efficiency test and leave-one-out sensitivity test. Immunohistochemical staining was performed using brain sections of mice infected with tissue cysts of Wh6 strain for image analysis using Image J software. Results A total of 29 SNPs were associated with toxoplasmic encephalitis. The results of IVW method suggested thatT.gondiiinfection made encephalitis risk 0.98 times higher(OR=0.98, 95%CI=0.76 to 1.27), indicating no causal relationship between the two. The quality control results suggested that the selected SNPs were stable and reliable.Toxoplasmacysts were distributed in various parts of the brain tissue. Conclusion T.gondiiinfection and encephalitis are related, but there is no sufficient evidence to prove the causal relationship between the two.