The caries activities of some commercially available children's beverages were measured to determine the risk of dental caries and provide basic data for preventing dental caries. For the experimental beverage, the beverages with the highest market share among carbonated beverages, fruit beverages, milk, and fermented milk products sold in the domestic market were selected. As a control, 0.25% glucose trypticase soy broth was prepared and used. The pH of the beverages, titrate acid and buffering capacity, and the acid production and vitality were measured over time after inoculating the beverages with Streptococcus mutans. The pH of children's beverages was the lowest in soda (2.61±0.02), and milk had the lowest in titratable acid (14.00±0.58). Fermented milk (80.33±3.64) had the highest buffering capacity, and carbonated beverage (9.40±1.06) had the lowest (P<0.05). Carbonated beverages (3 hr and 25 min) had the highest acid production, and milk (4 hr) had the lowest. In conclusion, thorough oral hygiene management is necessary after consuming children's beverages because they have a low pH promote high acid production of S. mutans.