The aim of the study was to predict loneliness with regard to parental acceptance-rejection and sibling relationship quality after controlling for gender, age, grade, school type, feld of study, birth order, and number of siblings. The UCLA Loneliness Scale, Maternal and Paternal Acceptance-Rejection Questionnaire, and Sibling Relationship Questionnaire were administered to 1,451 high school students, and multiple hierarchical regression analysis was conducted. Results showed that 1.7% of variance was explained by model 1, including demographic variables, but model 1 was not signifcant. After adding mother and father acceptance to model 2, the explained variance increased to 18.1%. In model 3, sibling variables were added and the explained variance was 19.6%, which were both signifcant results. Mother acceptance was the best predictor of loneliness, followed by father acceptance. Parental variables explained loneliness better than sibling and demographic variables. Understanding the family predictors of loneliness may be seen as the frst step for a subsequent intervention.