Objective: Vitamin B12 deficiency, an essential vitamin for the human body, is common in Turkey, and infants are at risk in this regard. This study was intended to investigate the effect of vitamin B12 levels of breastfeeding mothers with infant vitamin B12 and homocysteine levels. Material and Methods: A total of 214 infants aged 1-6 months and their mothers who applied to the infancy outpatient clinic of İstanbul Medeniyet University Göztepe Training and Research Hospital were included in the study. In this study, vitamin B12 levels of the mothers, vitamin B12, folic acid, and homocysteine levels in the infants were primarily analyzed, and the associated risk factors were secondarily determined. Results: The rate of adequate vitamin B12 levels in infants was 20.09% (n=43), and the rate of normal homocysteine levels in mothers of infants with sufficient vitamin B12 and normal homocysteine levels was 383.93 pg/mL and 379.07 pg/mL. 66.27% sensitivity and 75.56% specificity were calculated when 220 pg/mL was taken as the vitamin B12 cut-off value, which predicts homocysteine elevation. Conclusion: This study predicted that only one in five infants had sufficient vitamin B12 levels, but if breastfeeding mothers had sufficient vitamin B12 levels, infants were much less likely to have vitamin B12 deficiency. Since adequate vitamin B12 levels are important for infants, especially in terms of neurodevelopment, we believe that it is necessary to evaluate pregnant women in our society in terms of vitamin B12 levels and to provide vitamin B12 support.