Abstract: Objective To understand the type of clustering of pertussis cases in Tianjin and the Transmission characteristics of pertussis in expanded immunization era. Methods Passive surveillance in hospitals and active surveillance in communities were conducted in Tianjin, and descriptive epidemiological analysis was done on the surveillance data of pertussis. Results Four types of pertussis case clustering were found in Tianjin, The major one was household clustering (85.33%), but different clustering may co-existed. The transmission route in a household was mainly from adult to young child (67.19%) and parents were the major infection sources (78.44%). The attack rate in households was 77.88%. The infection rate in schools was as high as 64%. Clustered pertussis cases also occurred in staff in medical institutions. Conclusion The incidence and transmission patterns of pertussis have changed in expanded immunization era. It is necessary to conduct targeted pertussis surveillance, detection and prevention.