© 2021 Elsevier LtdBackground: Developmental disabilities (DD) in close family members have profound effects on psychological adjustment of siblings of individuals with DD. One factor that influences the psychological adjustment of siblings is emotions. However, little is known about emotions among siblings of individuals with DD. Aims: This study sought to examine negative emotions of adolescent siblings of individuals with DD and focus on the roles of individual- and system-related factors, namely early maladaptive schemas (EMS) and system justification. Methods and procedures: A cross-sectional study including adolescent 72 siblings of individuals with DD and 109 adolescent siblings of individuals without DD was conducted. Outcomes and results: The siblings of individuals with DD had higher scores on the Other-Directedness schema domain and system justification than the siblings of individuals without DD. However, the frequency of negative emotions did not differ between groups. Lower scores on EMS and higher scores on system justification were associated with less frequent negative emotions. Conclusions and implications: Negative emotions seem to be common in adolescents regardless of having a sibling with DD or not. Nevertheless, EMS and system justification tendencies in siblings of individuals with DD may act as vulnerability factors for negative emotions.