Theory suggests that children’s developing conceptions and views of relationship are important outcomes of social experiences, which can affect later relationships and mental health. However, research has been limited because no measure is currently available that captures children’s pessimistic and optimistic expectations of relationships. Two studies were conducted with children (aged 9 to 12 years) with the purpose of developing such a measure (Study 1 n = 226; Study 2 n = 200). Exploratory and confirmatory analyses resulted in a final measure that included eight items measuring optimistic relationship expectations and eight items measuring pessimistic expectations. The two subscales formed distinct factors were moderately correlated, and were reliable and valid when tested against measures of rejection sensitivity, social competence, relationships with peers and parents, personality, and self-presentation. The new Children’s Optimistic and Pessimistic Expectations of Relationships Scale (COPER) will be useful in future studies testing children’s relationship expectations.