Abstract: Objective　To confirm three severe scrub typhus patients in Mianyang of Sichuan Province using laboratory diagnosis and analyze their clinical characteristics to provide theoretical evidence for the prevention and treatment of scrub typhus in this area. Methods　From June 2021 to August 2022, blood specimens and clinical data were collected from three severe scrub typhus patients in Mianyang of Sichuan Province. The epidemiological history was surveyed and the collected clinical data were analyzed. Acute-phase whole blood, serum samples at admission, and convalescent-phase serum samples two weeks later were collected, and the IgG titers of anti-Orientia tsutsugamushi were detected by indirect immunofluorescence assay (IFA) assays. Total DNA was extracted from anticoagulation whole blood using DNA extraction kit, and semi-nested polymerase chain reaction (PCR) was used to amplify the special gene of O. tsutsugamushi. Phylogenetic trees were constructed using the maximum likelihood (ML) method to determine the genotype of the strains. Results　The clinical symptoms of these three patients were extremely similar to other infectious febrile diseases, with two cases showing obvious eschars on physical examination and all three cases causing pneumonia. Epidemiological investigation revealed that all had a history of wild animal exposure or fieldwork. Specific IgG antibodies to O. tsutsugamushi tests showed that convalescent serum antibodies increased by four times or more compared to the acute-phase serum. The TSA56 gene sequence fragment was obtained by PCR amplification, and BLASTn comparison on the NCBI website showed a close phylogenetic relationship with the TA763 genotype and Karp genotype of Orientia tsutsugamushi. The results indicated that these three cases were indeed infections of O. tsutsugamushi. Conclusions　Laboratory diagnosis confirmed the clinical diagnosis of severe scrub typhus in three patients, providing specific evidence of etiology. This is the first report of etiology-confirmed cases of scrub typhus in Mianyang City, Sichuan Province. Analyzing their clinical features as well as the genotypes is of guiding significance for early diagnosis, differential diagnosis, and adjuvant therapy of scrub typhus in this region.