From 1952 to 1953, in the agricultural and mountaineous villages of Okayama Pref. and Hiroshima Pref., an investigation was made about the actual state of "Weaning food" for infants and its effect exerted upon their bodily development both at the period fo weaning and at the later period of infancy; 520 infants (0-2 years old) and 626 infants (3-7 years old) were used as the subjects of investigation, giving the following results: (1) Of the 520 infants chosen (0-2 years old), the percentage of undernourished infants changed monthly as follows: (0-6 months old) 21%; (7-12 months old) 25%; (1-2 years old) 33.9%. Thus the percentage rose highest at the weaning period. (2) In the monthly change in infants' body-weight, the percentage of growth was rather low at the weaning period, the boy babies showing 80% of the standard value and the girl babies 89%. (3) The research on the actual state of weaning in those regions of Japan revealed that the starting time and the weaning food used then were almost proper, but that the delay in the development of staple chief food taken and the lack in protein taken were quite remarkable. (4) It was fonfirmed those infants who were not properly weaned were suffering from malnutrition far more than those who were properly weaned. (5) Among those who were delayed in weaning, move underdeveloped infants were found than in other cases, but it seems not to be reliable from the viewpoint of sampling statistics. Such a correlative relation as seen between the body-weight at birth and the growth of infants in the later period could not be found.