From April through July 1988, an epidemiological investigation on Lyme disease was carried out in Nalati Xanyuan, Xinjiang Uygur Autonomous Region, China. Of 150 Ixodes persulcatus ticks examined by darkfield microscopy, 42 (28%) were found to have spirochetes. Two strains of spirochetes were isolated from I. persulcatus with BSK medium. Rabbits inoculated with the spirochetes showed erythema chronicum migrans at the sites of inoculation and the spirochetes were found in the cerebrospinal fluid by darkfield microscopy. Serum samples from 63 patients were examined for antibodies to B. burgdorferi by IFA test and 11 of them were positive with a titer of 1:64. Upon these results, it may be concluded that natural focus of Lyme disease exists in Xinjiang, China.