Cow's milk containing approximately 0.54 μg of B₁₂/100 g of milk is an important source of B₁₂ in our diets. Although some studies have reported the effects of heat processing on B₁₂ in milk, kinetic studies regarding the thermal degradation of this vitamin are still scarce. In this study, the kinetics of thermal degradation of vitamin B₁₂ in cow's milk were obtained in the temperature range of 102.5–141.6 °C and holding times up to 1200 s. The results showed that the degradation of B₁₂ in milk followed a first-order kinetic reaction in the range of temperature tested. The Arrhenius model with an activation energy of 130 ± 5 kJ/mol and was successfully used to predict few data reported in literature for B₁₂ degradation in milk. Compared with other foods, our results suggest that the milk matrix may protect B₁₂ from thermal degradation.