Abstract: Objective To investigate the prevalence of tickborne rickettsial diseases(TBRD) and its dynamic trend in Tianjin during 2007-2009.Methods Eight districts in Tianjin were selected as study sites,and blood samples from study subjects were collected each year during July to September.A total of 886 study subjects were recruited using a cluster sampling method from 2007 to 2009.Blood samples were tested with indirect immunofluorescence assay for lgG antibodies against Anaplasma phagocytophilum,Rickettsia sibirica and Ehrlichia Chaffeensis.Results A high prevalence of human granulocytic anaplasmosis(HGA) was detected among the 8 study sites,with the highest in Dagang district(57.7%,2008) and Dongli district(70.6%,2009).The prevalence increased by 33.3 percent within the 3 years.Seroprevalence of human monocytic ehrichiosis(HME) varied from 2.6%-4.4%,and the most of the cases were detected in the center and sourth area.The prevalence of spotted fever group Rickettia(SFGR) was low(1.6%-2.0%) and more common in the center and north area of Tianjin.Conclusion TBRD,especially human granulocytic anaplasmosis,were common in Tianjin,and the prevalences showed a diverse trend in different districts.