Purpose: The purpose of this study was to identify the relationship of peer relationships, self-reported attachment security, perceived parental rearing attitudes, and loneliness in upper elementary school-age children. Methods: The data were collected from 207 students in grades 5 or 6, and descriptive statistics, t-test, Pearson correlation coefficients and Stepwise multiple regression were used with the SPSS/PC 12.0 program to analyze the data. Results: There was a significant difference in loneliness between the upper 25% and lower 25% groups of peer relationships, perceived parental rearing attitudes, and self-reported attachment security. Stepwise multiple regression analysis showed affection-hostility in parental rearing attitudes, validation and conflict in peer relationships, and attachment security explained 39.6% of the total variance in loneliness. Conclusion: These results may contribute to a better understanding of loneliness in upper elementary school-age children. The results of the present study indicate a need to develop nursing interventions to prevent and manage children‘s loneliness.