The purpose of this study was to investigate the relationships between interpersonal behaviors and duration of three-year-or two-year-preschool enrollment. Sixty-eight three-year-enrollees and 25 two-year-ones from a Kurahashi program kindergarten served as the subjects. They were observed six times between the first term of four-year-class and the third term of five-yearclass. Each observation consisted of 20 minutes. Three-year-enrolled boys had more samesex ties and task-oriented solitary behaviors than the other categories across all terms. Twoyear-enrolled boys employed same-sex pairs and same-sex groups after engaging in immature solitary behaviors. On the other hand, three-year-enrolled girls participated in more same-sex pairs than the other categories. Two-year-enrolled girls developed same-sex pairs and samesex groups after engaging in unoccupied behaviors and same-sex groups with teachers. As the child adjusted to the kindergarten environment, he/she skillfully used same-sex groups, same-sex pairs, solitary behavior and parallel behavior, or mixed groups. Controversies over the relationship between the duration of preschool enrollment and development of interpersonal behaviors have been one of interests to teachers, parents and researchers.Macrae and Herbert-Jackson (1976) found that children with more day-care experience got along better with their peers than did children with less day-care one. Vlietstra (1981) reported that, according to naive observers, two, three and four-year-olds who were full-time attendees in Montessori schools spent significantly more time working on teacher-directed tasks and interacting positively with their peers than did children who only attended parttime. However, their teachers rated the full-time attendees as less cooperative with their peers than did the counterparts.Schwartz, Strickland, and Krolich (1974) also reported that children, with greater amounts of group experience, were less cooperative with adults. This effect was apparently a result of adjustment patterns. As the children adjusted to established groups, they became more assertive and adults, in turn, made more efforts to control them. As a result, the teacherchild relationship deteriorated. McGrew (1972) found that newcomers initially showed passive interpersonal behaviors and engaged in unoccupied activities, but they soon adjusted to an established group. Feldbaum, Christenson, and O'Neal (1980) observed that three and four-year-old children adjusted to established groups within four weeks. As a result, newcomers initially displayed solitary behavior or off-task activity, but the hosts were more likely to use parallel and cooperative behaviors. In addition, while fresh boys approached same-sex peers, fresh girls showed more solitary or unoccupied behaviors and sought more interaction with adults. Moreover, while boys