This study was aimed at describing transformation of a girl (5-years-old) in peer relationships in her preschool. In the study 1, the subject was observed in free play during two terms, the first term(from April to July) and second term(from October to February). The view points of the observation were social skills of the subject and interaction from others (teacher, peers). In the study 2, social-psychological adjustments were assessed. Results indicated that the subject was provided little pro-social behavior from peers than other children. Teacher supported her to join peers through one year. In the first term, she hardly interacted with peers. But, in the second term, her interaction with peers greatly increased from first term to second term.