In an outbreak of scrub typhus occurred 138 cases in 1986 in Menying County of Shandong Province of China which were confirmed through clinical and epidemiological surveys and laboratory techniques. In the endemic areas, the predominant species of mite is Leptotrombidium (L.) scutelarae and the predominant rodent is Apodemus agrarius, which may be the main vector and reservoir. Several strains of Rickettsia tsutsugamushi (R.T.) were obtained from mites, wild mice and patients, of which 3 human strains (SDH871, SDH875, SDH878) cause illness and some deaths in mice, except SDH871. The LD50 of SDH878 is 3.4. Cross-protection was observed among the strains, SDH871, SDH878, and prototype strain karp. Also the antibodies in mucoid peritoneal fluid were detectable with high titer. Shandong R.T. belongs to the serotype of the Gilliam strain.