The study was conducted to examine the effectiveness of the Imo state vigilante service in promoting community security in Isiala Mbano local government area of Imo state. In order to achieve the purpose of the study, five research questions were raised and answered. The study adopted the descriptive survey research design. The population of the study consisted of seventy-five (75) members of various groups in Isiala Mbano local government area. The multi stage sampling procedure was used to select a total of seventy-five (75) participants from various strata in the local government area under study. A questionnaire titled ―Effectiveness of the Vigilante Group in Promoting Community Security‖ (EVGPCS), focus group discussion guide (FGD) and in-depth interview guide were the instruments for data collection. Validity and reliability of the instruments were ensured. Data were anaysed using simple percentage, and mean. The IDIs and FGDs were tape recorded and transcribed verbatim. Findings revealed among others that Imo State vigilante service and the police force in the state have a professional relationship, the Imo state vigilante service carries out its function of crime control by collaborating with the police, combing hideouts in their environment, ensuring constant presence of Imo State Vigilante Service men in the community and swift reaction to imminent security challenge and that Imo state vigilante service is moderately effective in providing security for communities in the area. Based on the finding, it was recommended that local government authorities and the police force should provide necessary support to the IVS in their area by organizing seminars and workshops on the issue of crime for youths in the area. Local government authorities, non-governmental organizations in the area and well-meaning indigenes should assist the IVS with logistics that will aid their patrol activities. More training and retraining programme should be organized for the IVS by men of the police force so as to enable them meet up with the demands of combating crime in their locality.