Abstract. Diphtheria in Bangkalan Regency is the third highest in East Java. The highest diphtheria cases in the last 5 years occurred in 2018. Until the end of January 2019, there had been 4 cases of diphtheria outbreaks, in which 2 cases of the toxigenic laboratory were confirmed positive. The purpose of this study was to determine the priority and root causes of immunization and to be used in planning and implementing a diphtheria control program appropriately.This was an observational descriptive study conducted at the Bangkalan District Health Office in January 2019. Problem identification was carried out using the Nominal Group Technique method. The determination of priority problems was done by using the Capability, Accessibility, Readiness, and Leverage (CARL) method. The root cause of the problem was done using a fishbone diagram. The priority problems detected were coverage of basic complete immunization and Diphtheria Pertussis Tetanus (DPT) Booster immunization for the last 3 years had not met the target and was not evenly distributed.The priority of the root of the problem is that the village immunization coordinator is not good at collecting data on the number of targets and does not conduct education before immunization. Immunization coordinator training at the village or private level is still limited. Strengthening the role of village immunization coordinators involving other sectors and the formation of community empowerment programs is also limited.