Infant formula in nursing bottle, with inappropriate feeding habits, is major factor associated with the development of nursing caries. Although each infant formula has different carbohydrate and protein composition, studies comparing cariogenic potential of many Korean-branded infant formulas are deficient. In addition, it is on the point of being difficult to evaluate the cariogenecity of milk due to development of many infant formulas. In this study, to evaluate the cariogenic potential of many infant formulas, after oral rinse with six Korean-branded infant formulas(three milk based formulas, one soy based formula and two specific formulas for infants with allergy to milk protein and with lactose intolerance) for ten adult volunteers(eight males and two females), plaque pH change was measured with In vivo/In vitro combination technique and results were as follows. 1. All six different kinds of Korean-branded commercial infant formulas dropped the plaque pH significantly(p<0.05) and at an hour after rinse, plaque pH was not recovered in most of subjects. 2. Soy based infant formula and casein-hydrolyzated infant formula containing no casein dropped the plaque pH significantly more than milk based infant formula containing casein (p<0.05). 3. In the milk protein of infant formulas, casein had more effect on buffering the pH change of the infant formula than whey protein and casein-hydrolyzated infant formula had a reduced effect of casein. 4. In infant formulas with similar protein composition, infant formula containing sucrose dropped plaque pH more than infant formula containing lactose, but there was no significant difference (p>0.05).