Immunization during childhood has been proven to be the most effective strategy for the prevention of many infectious diseases. The aim of this study is to assess vaccination coverage and identifying factors that affect full immunization of children of the age between 12 and 23 months in Ethiopia. Data for the study were obtained from 2005 Ethiopia Demographic and Health Survey (2005 EDHS). Classical logistic regression analysis was used to investigate the relative importance of demographic, socio-economic, and other variables in determining the full child immunization status and Bayesian logistic regression also used to see the effect of those variables and to compare it with three different prior variance. Results of the study showed that the coverage of full vaccination varies across regions, the highest in Addis Ababa (64.1%) to the lowest in Afar (0.9%), and it also showed that respondent who live in rural area had only 14.6% chance to fully vaccinate their children. the concerned body should give attention for people who live in rural area and hard to reach regions.