A total of 1316 subjects (658 males and 658 females), aged from 16 to 66, rated themselves against a set of 65 selected scales of a questionnaire constructed to measure physical, intellectual, emotional and social aspects of adult characteristics. By assigning plus one to an affirmative response by the subjects to each scale, minus one to a negative response, and zero to an undecisive response. Adult Scores (A. S.) for all age-groups were calculated, and inspection of these A. S. thus obtained indicated that, there were 28 effective items with males and 19 effective items with females. Although there were wide individual differences in each age group, adult characteristics were, in general, reached in the male groups between the ages of 25 and 29, and in the female groups, between 30 and 34. Greater individual difference in terms of S. D. was found in the male groups than in the corresponding female groups. From the shapes of the A. S. curves plotted across the age-groups, six types of development of adult characteristics were confirmed. Inter-scale relatedness as indicated by the percent agreement (70% or above) between each pair of the scales was more often found in the male groups than in the female groups. Adult characteristics were further analyzed concerning the specific nature of each of the four aspects, as stated above of personality development, and the implications derived therefrom were discussed in details.