The purpose of this study was (1) to find the 5 patterns of the conversational competence in the field of the language development of twins, and (2) to descrive the concrete examples which could be seen in their daily lives. The 5 groups of cognitive competences and in conversation are as follows: 1) A recognition of speaker's intention: They can answer utterances based on their understanding of the speaker's intention. 2) A cognition of self awakening: They can understand the speaker's attitude and then insist on their purposes. 3) The use of rethoric: They can talk with nature and animals. 4) Their mutual interference: They try to imitate the expressions from each other. 5) The generalization of the words learned already: They generally use to apply the learned expression to others. Those 5 competences are interrelated with each other. How to choose their patterns differs individually.