PURPOSE: This study was undertaken to compare the mental and motor development, unsing Bayley Developmental Scale, during infancy(6-8 months of age) according to the choice of feeding, either breast milk of formula, as well as to evaluate its influence on physical growth. METHODS: The study population was 43 normal infants between 6 and 8 months of age, of birth at gestational ages between 37 and 42 weeks, and with birth weights greater or equal to 2500g and below 4000g, excluding high risk infants who were liable for poor neurological prognosis. The breast-fed group was defined as those whoe were breast-fed for at least 3 months after birth. Bayley Developmental Test was performed using Bayley Scales of Infant Development(BSID) test kt. To obtain the data for the analysis of factors influencing the choice of feeding, we used questionnaires. We also measured height, weight, and head circumference for the evaluation of physical growth. RESULTS: We analysed statistically the influence of the educational status of mother or father, the occupational status of mother, birth rank, sex and the mode of delivery on the choice of fedding, but there were no factors causing and significant difference between the breast-fed group(n=22) and the formula-fed group(n=21). The MDI's of the breast-fed and the formula-fed were 101.0 and 103.0, respectively, while the PDI's were 104.2 and 107.0, respectively, There was no statistical difference. The mean height, weight, and head circumference were greater in the breast-fed group but wighout statistical significance. CONCLUSIONS: We may cautiously conclude from the given results that the choice of feeding would not have a great impact on the growth and development of infants.