Purpose: To investigate the effect of different milk formulas on dental plaque pH. Materials and Methods: Six commercial infant milk formulas were selected, with 10% sucrose solution as the positive and deionised water as the negative control, and tested among ten children aged 7-10 years. The plaque pH changes were recorded by using a combination electrode. Results: Mouth rinsing with all infant formulas significantly reduced the plaque pH (Tukey's multiple comparison test, P 0.05) to levels below the pre-rinse pH value for sucrose solution and also below the pH obtained after rinsing with water. Each milk formula had a significant but variable buffering effect or tendency to decrease the pH. The formula with the least buffering effect was Nestogen (9.21%) followed by Nan (11.92%), and the highest buffering effect was shown by Lactodex (20.13%). The pH drop ranged from 0.72 for Farex to 0.98 for Nan. Conclusion: The results of this study underscore the need for parents and clinicians to be fully aware of the potential harm of various infant formulas and their major role in the etiology of ECC. These findings may help in creating a new generation of foods which, if not 'friendly to teeth', may be thought of as 'friendlier' than their predecessors. Keywords: baby bottle tooth decay, early childhood caries, infant milk formulas, plaque pH