Objective: To evaluate the efficiency of the sublingual route for the treatment of vitamin B12 deficiency in infants. Background: Vitamin B12 deficiency is common in children. In breastfed infants, the main reason is maternal B12 deficiency. Parenteral administration is commonly prescribed. However, patient compliance is not satisfactory due to repeated painful parenteral applications. It is also known that the oral route is efficient in high doses. In recent years, the sublingual route has been tried. This route stands out due to its easy applicability and low cost. However, there are few efficacy studies in infants for the sublingual route. Materials and methods: The study included 49 infants aged 6-12 months. All infants with marginal or deficient B12 levels (<300 pg/mL) were incidentally detected and treated with sublingual methylcobalamin. Each dose was 1000 mu g and administered once a day in the first week, every other day in the second week, twice a week in the third week, and once a week in the last week. Serum vitamin B12 levels were measured before and after the treatment. Paired Sample T-Test was used to compare variables. Results: All infants had normal physical development and had no hematological or neurological issues. It was learned from the parents that the infants tolerated treatment well, and no side effects related to the treatment, such as vomiting or rash, were observed. Before and after the treatment, the mean vitamin B12 levels were 199 +/- 57 pg/mL and 684 +/- 336 pg/ml, respectively. The difference between the means was statistically significant (p<0.001). Conclusion: According to the study, it seems possible to treat vitamin B12 deficiency via a sublingual route in infants. In addition, methylcobalamin can be an alternative to the commonly used cyanocobalamin.