To characterize the epidemiology of autumn-winter type scrub typhus in a new endemic focus of Fei County, Shandong Province, China, field and laboratory studies were conducted to determine the species composition and seasonal fluctuations of chigger mites and their animal hosts. Orientia tsutsugamushi was isolated, and serotypes of antibodies to O. tsutsugamushi were detected and identified. A total of 1044 rodents and insectivores were field collected: 751 Apodemus agrarius (71.94%), 266 Tscherskia triton (25.48%), 1 Cricetulus barabensis (0.09%), 11 Rattus norvegicus (1.05%), 3 Mus musculus (0.29%), and 12 Crocidura suaveolens (1.15%). Apodemus agrarius, T. triton and R. norvegicus were shown to be naturally infected with O. tsutsugamushi. The serum antibody positive rate of rodents was 14.78%. A total of 11762 chigger mites were collected: 2547 Leptotrombidium scutellare (21.65%), 1596 L. palpale (13.57%), 466 L. taishanicum (3.96%), 2833 L. linhuaikongense (24.09%), and 4320 Walchia pacifica (36.73%). Leptotrombidium scutellare was most numerous from September to November and was the predominant species during the local scrub typhus epidemic season. Natural infection with O. tsutsugamushi was detected in L. scutellare, and transovarial transmission of the pathogen by this chigger was demonstrated. 38 strains of O. tsutsugamushi were isolated from 33 patients (14 strains), 3 species of rodents (9 strains), and 4 species of mites (15 strains). All O. tsutsugamushi strains isolated in this endemic focus were of low virulence. Serotype identification showed that 33 strains were of the Gilliam type, and 3 strains were of the Karp type. Another 2 strains remain to be identified. In the Fei County focus of scrub typhus, the main reservoir host is A. agrarius, the predominant mite vector is L. scutellare, the principal serotype of O. tsutsugamushi is Gilliam, and all strains of O. tsutsugamushi are of low virulence. Most cases of scrub typhus occurred from September to November; therefore, scrub typhus in this focus is autumn-winter type. This focus is located in the premontane flatlands of Fei County.