Rickettsia tsutsugamushi, a causative agent of Tsutsugamushi disease, is transmitted to human by Leptrotrombidium mites. In the initial part of this review, we describe a relationship between the rickettsia and vector mites, especially on the vertical transmission mechanism of the rickettsia in the mites. In the later part, new findings on R. tsutsugamushi will be reviewed, especially on the classification of this rickettsia, antigenic type-variation and correlation of this antigenic type to mites, and the molecular analysis of the type-specific antigens.