Background: Studies have demonstrated that high vaccination coverage rates do not necessarily imply valid dose vaccinations. The timely start of vaccination is important in light of the rapid waning of trans-placental immunity in the first year of life against vaccine-preventable diseases. Delayed doses in turn put individuals at risk of disease due to waning immunity over time and put the whole community at risk of epidemic. The valid dose of vaccination for children is important to build baby's immunity at an early age in order to reduce his/her risk of serious disease or death. Thus, it is important to take the valid dose of vaccination into account. Objective: Assessment of the magnitude of valid dose of child vaccination & its associated factor among children aged 12 – 23 months in Duguna Fango woreda, wolayta zone, Southern nation & nationality people region, Ethiopia, February 10 – 29, 2016. Methodology: Community based cross sectional study was conducted in Duguna fango woreda, Wolaita zone from February 10 - 29, 2016 G.C. A total of 491 children of aged between 12-23 months with vaccination card & registered in health faccility vaccination registration book is included in this study. World health organization cluster sampling techniques was used to identify study units. Data were obtain from vaccination cards & registration book from vaccinated health facility. Information on maternal socio-demographic characteristics and household variables were collected using an interviewer-administered structured questionnaire. Data were entered and analyzed using SPSS version 20. Bivariate analysis was done to test the association between independent and dependent variables. Variables with P<0.2 in the bivariate analysis were included in multivariate logistic regression to determine the valid dose of childhood vaccination. Result: From total of 491 children included in the study only 32.2% (95%CI: 28.1, 36.0) are found to have valid dose vaccination. Mother’s educational status with AOR of 1.86 (0.86, 4.0), Income 3.62 (0.98, 3.39), caregiver’s age 3.22 (0.17, 60.2), knowledge on session’s time specifically on the second session time AOR=5.2 (95% CI: 1.26, 29.4), quality and accessibility to health facility 15.12 (1.54, 148.05) & Proper appointment given with AOR of 41.63 (4.45, 388.73) were the main factors associated with having a valid dose vaccination of children aged b/n 12 – 23 month. Conclusion: There is low magnitude of valid dose vaccination among children aged 12-23 months in Duguna Fango woreda. Hence Wolaita zone health department, Duguna fango woreda health office & the health facilities under these woreda should work strong and intensive awareness creation activities on these mentioned contributing major factors above to improve a valid dose vaccination of children in their area and acquire quality vaccination service to the community