In the southeast coast of Shikoku, most of the Japanese spotted fever (JSF) patients were found to be infected with the rickettsial pathogen through bamboo plantation, and also the eschar was frequently noticed in skin inspection, so that it was clinically speculated to be caused by ticks. According to out field research, the tick fauna was very rich throughout that area, and it was permissible enough to determine ticks as the vectors, based on arising of and-SF group rickettsiae (SFGR) antibody in mice inoculated with some tick emulsions, findings of rickettsiae reactive to patient sera or a species-specific monoclonal antibody to JSFR in the hemolymph cells of some ticks, and electron microscopical observations of SFGR in various internal organs including the salivary gland of ticks. Also the transovarial and transstadial transmissions of SFGR in ticks were supposed. Our results suggest that common species (adult/nymph) of the genus Haemaphysalis may be the most related vectors to man, based on their dominances, SFGR-prevalences, behavior and incidences of infestation but also indicate that various genera and species should be kept as the potential vectors, in spite of JSFR isolation from a restricted species of ticks in the future.