Mate value represents the overall characteristics of a person important for successfully finding, attracting and retaining a partner. People are usually aware of their own and their partner's value, as well as the existence of a discrepancy between them. Previous research has established a negative association between the aforementioned discrepancy and relationship satisfaction. Inclusion of other in the self refers to the degree to which perception that people have about themselves overlaps with their perception of close others. So far, the relationship between the mate value discrepancy and the inclusion of other in the self has rarely been the subject of research, but their negative association is assumed. Self-expansion can be achieved by forming and maintaining close relationships in which the partners' perspectives, resources, and identities become to some extent included in the self. Previous research has established a positive association of self-expansion encompassing the inclusion of other in the self and relationship satisfaction. Considering the lack of research on this topic on the Croatian sample, this study aimed to determine the contribution of the mate value discrepancy and self expansion in explaining the variance of inclusion of partner in the self and relationship satisfaction. Data collected in a sample of 463 adults who are in a romantic relationship were used to examine the problems. The data were collected through an online questionnaire including general questions about participants (sex, age) and romantic relationship they were evaluating (how they consider current relationship, relationship duration, duration of knowing partner before the beginning of the relationship), Inclusion of Other in the Self Scale (Aron et al., 1992), Mate Value Inventory (Kirsner et al., 2003), Self-Expansion Questionnaire (Lewandowski and Aron, 2002) and adapted version of Marital satisfaction scale (Ćubela Adorić and Jurević, 2006, according to Ćubela Adorić et al., 2014). A positive correlation was found between self-expansion and mate value discrepancy. Each of the mentioned variables is positively related to the inclusion of partner in the self and relationship satisfaction. The obtained results point to the self-expansion as the only significant positive predictor of the inclusion of partner in the self. Furthermore, mate value discrepancy and self-expansion were shown to be significant positive predictors of relationship satisfaction with the fact that the self-expansion has a greater contribution to the explanation of the variance of relationship satisfaction. Given the importance of the direction of the mate value discrepancy in understanding different relationship outcomes, differences in individual variables between participants in dating up and participants in dating down relationships were also examined. Participants in a dating up relationship evaluate selfexpansion, inclusion of partner in the self and relationship satisfaction as higher than participants in a dating down relationship.