The authors tried to clarify in Vol. 2 No. 2 that there were some personality differences between member of a pair of identical twins (EZ). Some of these differences were reduced to those of elder-brother-like and younger-brother-like characteristics as seen between non-twin siblings. In Japan there is a great difference in the treatment of the child depending upon his position in the family. In this research as attempt was made to study the relationship of the personality differences between identical twins and their treatment by the family in light of the above mentioned fact. As the first approach the following questionnaire was made. 1. Do you treat the twin differently ? 2. Is the order in which baths are taken or the seating at the dinner table strictly followed in your family ? 3. Do you treat the elder as the superior ? 4. When they quarrel do you arbitrate or scold based on the reason that they are the older or the younger ? 5. Which did you feed first during infancy ? 6. Which did you bathe first during their infacncy ? 7. Which of them do you wake first in the morning ? 8. Which do you serve first at meals and at snack time ? 9. Which do you call first when you call them at the same time ? 10. Which do you introduce first to others ? 11. Then there is an important errand to be done which one do you ask to do it ? 12. Which do you ask to preform simple errands ? 13. Which do you consult about important matters ? 14. At the present which do you depend on more ? 15. Which do you expect to be more successful in the future ? 16. Do the children feel that they are being scolded as the elder or the younger when they quarrel ? 17. Do the children feel that that they are treated as the elder or the younger ? 18. Are the twins aware that one is the elder and and the other is the younger ?