Purpose: To study effects of the attitude of mothers in rearing the infants upon the mental development and to analyze factors connected with the maternal attitude.<BR>Subject: Healthy infants born normal and with full-term and their mothers were selected at two out-patient clinics. The numbers of the subjects were a hundred and twenty mothers and their infants, about thirty at each age level of 2, 6, 9, and 12 months old.<BR>Method: 1) To study the maternal attitudes, the mothers were interviewed to be asked in twelve infant-rearng situations such as feeding schedule, the practice of mothers when infants cried, finger-sucked, or made mess at dinner table etc. Behaviors of mothers and children during interview and test were recorded on a form prepared. Opinions on childrearing were asked on eight statements which concerned with permissiveness and indulgence. Materials concerning with mother's attitudes were summarized on a card for each person and were independently evaluated by two people according to seven factors which turned out to have constructed mother's attitudes on this age level. Those were emotional security, contact with infants, concern with rearing, permissiveness or regulations of children's activities, forms of mothers and infants, intellectuality, previous attitudes of the mothers.<BR>2) To study the mental development of children, a questionnaire scale of infant development, constructed by the authors on the basis of following up study of three infants for a year, was used The scale is consisted of a hundred-and-ninety developmental items which can be observed easily in daily living situations by an ordinary mother. Developmental test standarlized by Ushijima in 1938 was used. at the same time.<BR>Result: 1. Relationship between mother's attitudes and infant's development.<BR>(1) Two months old; When mothers have more contacts with infants, motor and social development tended to be better than those with less contacts with. infants, but with no statistical significance.(2) Six months old; When mothers have more contacts with infants and are more permissive, social development and feeding behavior tended to be more superior than those with less contact and less permissiveness with statistical significance under 1% level.(X2 test)<BR>(3) Nine months old; When mothers have more contacts with infants and are more permissive, social development, exploring behavior and activities of infants tended to be more suprior with statistical significance.(4) Twelve months old; When mothers have more contact and are more permissive, exploring behavior and activeness of infants tended to be more superior, but with no statistical significance.<BR>2. Factors relating to the maternal attitudes.<BR>(1) There was no apparent relationship between maternal attitudes and socio-economic status.(2) In an upper socio-economic status, the opinions on child rearing were less permissive and more indulgent (3) There was no apparent relationship between maternal attitudes and opinions.(4) For the first-born infants, maternal attitudes and opinions tended to be more permissive.(5) Maternal attitudes tend to get more permissive when the age progresses, during the first year.<BR>Conclusion: We could conclude from the results described above that infants tend to develop better when mothers have more contacts with children and are more permissive, than when mothers have less contacts with children and are less permissive.