Introduction: Vaccine preventable disease remained issue of major concern to the global health system. Low coverage of immunization necessitated the need to explore the determinants of immunization uptake. Factors influencing immunization coverage in South-West Nigeria were investigated in this study. Methods: Data from the Nigeria demographic and health survey (NDHS) was used for this study. Our focus was on children between 12 to 23 months whose parents were residents of South-West Nigeria. A total of 655 records were used for the analysis of this study. The outcome variable (child’s immunization status) was categorized as “non-or- under immunized and fully immunized”. Considered explanatory variables were children and parents’ characteristics. Data were analyzed using Statistical package for social sciences (SPSS) version 25. Descriptive statistics were presented and generalized linear model was used to explore the determinants of immunization completeness. Results: Of the 665 children whose mean age was 16.7 ± 3.4 SD months, 62.3% were non-or-under immunized, while only 79.8% were birthed in the health facility. Majority of them (65.1%) were not presented for postnatal check within two months of birth while 51% do not have health card. About 79% of the mothers said distance to the health facility was not a problem. In this study, postnatal check within 2 months of birth, type of residence and ownership of health card were identified factors influencing the uptake of immunization. For instance, Those who said distance is a problem were 3 times less likely to fully immunize their children (AOR=0.28, p=0.000, 95% CI: 0.16-0.47). Obviously, ownership of health card (AOR=15.34, p=0.000, 95% CI: 9.86-23.88) and postnatal check within 2 months of birth (AOR=1.78, 95% CI: 0.37-0.86) were associated with the likelihood of complete immunization. Conclusion: Immunization uptake was very low in South-West Nigeria. Factors that were positively associated with completeness of immunization include observance of postnatal check and ownership of healthcare card while problem of distance to health facility was negatively associated. Increasing vaccination coverage/ completeness would ameliorate, if policy geared towards the improvement of postnatal check-ups, distribution of healthcare facilities within residential areas and strict adherence to the use of health care are considered in the South-West Nigeria.