Vaccination is the epicenters of preventive care for good children health outcomes in each nation. Nevertheless, numbers of factors have been hindering the attainment of targets to provide complete vaccination in different nations. The aim of this study is to assessed predictors of immunizations in 12-23 months aged children in Abobo District, Gambela regions south west Ethiopia.Method: A community based cross-sectional study was employed in 436 pairs of mothers to children aged 12-23 months from 12 march -27 April 2019. The study participant were recruited by multistage-sampling were used for each kebele. Data were entered into Epi-Data version 3.1 after cleaned and coded, exported to STATA/SE-14/R analysis of logistic regression. Variables with P-value < 0.25 in bivariate logistic regression were transported in to multivariable logistic regression; a variable with 95% CI in AOR was used claim predictors for dropout rate. Results:The overall dropout rate of immunization from completion was found 25.8% (95% CI: 21.5-30.2). Factors like mothers did not attend ANC (AOR = 4.59, 95% CI: 2.58, 7.84), being home delivery (AOR = 6.46, 95% CI: (3.5-11.4), postponed last immunization scheduled (AOR = 3.44, 95% CI: 1.98-5.97), children ill during measles vaccine (AOR = 1.83, 95% CI: (1.02-3.28), Mothers refused ≥ 30 minutes for vaccine service waiting (AOR = 3.58, 95% CI: (1.99, 6.44) were significantly associated with immunization dropout out. Conclusion:The immunization dropout rate was unacceptable and higher as compare with WHO reference (< 10%). Home deliver, postponed measles vaccine, child illness, ANC status Service refusal ≥ 30 minutes waiting for vaccine were independently associated with dropout.