Purpose: The aim of this study was to evaluate the effectiveness of SYMBIS-based premarital training on marital differentiation, attitudes, and expectations among single girls of Hormozgan University. Method: This study was quasi-experimental research, pre-test-post-test design with a control group. The statistical population consisted of single girls of Hormozgan University those who scored lower on differentiation components, attitudes, and marital expectations, 32 people were selected through convenient sampling method, randomly assigned to experimental, and control groups (each group consisting of 16 subjects). The Nelson and Jones Marriage Expectation Scale, Skowron Differentiation, and Braaten & Rosé n Marital Attitudes Scale Questionnaire were used to collecting data. We performed an 8-session SYMBIS-based premarital training in experimental group. Findings: The findings showed that 1) SYMBIS-based premarital training had a significant effect on differentiation, marital attitudes, and marital expectations, as well as on emotional reactivity, cutoff, and fusion with others and pessimistic expectation, but it did not have a significant effect on "I position", Realistic and idealistic expectation; 2) SYMBIS-based premarital training had a significant effect on marital attitudes and marital expectations, emotional reactivity, cutoff, and fusion with others in follow up phase, but it did not have a significant effect on differentiation in follow up. Therefore, according to the content of this intervention, it can be used in promoting differentiation, improving youth attitudes, and reducing pessimistic expectations before marriage.