Background: Childhood vaccination is one of the most valuable public health interventions available for preventing childhood morbidity and mortality. Basic vaccinations are estimated to avert 2.5 million annual child deaths globally from diphtheria, tetanus, pertussis, and measles. Despite, EPI services exists in all kebeles and delivered by health extension workers to community, still there is high number of defaulters in Ethiopia particularly in the study area. Administrative reports of the past 2 years showed Bahir Dar Zuria district has high vaccination defaulters persistently. Even though, there are similar studies conducted in the Ethiopia, the factors contributing for incomplete vaccination were many and interwoven; and have not always been consistent across the study areas. Therefore, the aim of this study is to assess the magnitude and the real factors associated with incomplete vaccination among children aged 12–23 months in Bahir Dar Zuriya district. Objectives: To assess incomplete vaccination and associated factors among children aged 12-23 months in Bahir Dar Zuriya District, 2020. Methods and Materials: A community based cross-sectional study was carried out from February, 2020 to April, 2020 in Bahir Dar Zuria District, North-Western Ethiopia. The sample size was calculated for first and second objective based on sample size calculation for single population and 542 subjects were included for this study. A multi-stage sampling technique was employed. Data were collected using pre- tested interviewer-administered questionnaires and vaccination card. Data was entered to Epi-Data software version 3.1 and exported to SPSS version 23 software packages for analysis. Simple and multiple binary logistic regression analysis were computed to identify significant variables and to control possible confounding effect. Those independent variables which have P-value <0.25 in simple binary logistic regression have been considered a candidate variable for multiple binary logistic regression analyses. Variables with a P value of <0.05 in the multiple binary logistic regression analysis has been used to explain the presence of statistically significant associations. Adequacy of the model was assessed using Hosmer and Lemeshow goodness of fit test at p-value > 0.05 and presence or absence of multi- colliniarity was also checked. Results: A total of 542 mothers/caregivers with children aged 12 - 23 months old were interviewed for the study with a response rate of 100%. Of these, about 137(25.3%) of them didn’t complete their vaccination according to schedule for routine immunization. Place of residence [AOR=12.1, 95% CI: 3.86, 42.16)], place of delivery [AOR= 2.9, 95% CI: 1.771, 4.819)] and advice from health workers [AOR= 3.9, 95% CI: 2.335, 6.493)] were significantly associated factors of incomplete vaccination. Conclusion and recommendation: In this study the magnitude of incomplete vaccination was found to be 25.3% (95% CI: 21%, 29%). Variables that showed significant associations with children incomplete vaccination were maternal place of residence, place of delivery and ever receive advice from health workers. Therefore, greater emphasis should be given to the community awareness creation through health education on the importance of vaccination completion and promoting institutional delivery.