Background: Typically developing (TD) siblings play a crucial role in promoting the health and well-being of adults with intellectual disabilities. Their involvement in the sibling relationship during adulthood may predict their likelihood of providing care to the sibling with intellectual disabilities (ID). However, different types of motivations (discretionary and obligatory) related to the contact frequency of TD siblings have not been fully explored. Little is known about how their negative experiences, such as affiliated stigma, influences relational motivations, which consequently affect contact frequency. This study examined these links in a Chinese context. Method: In total, 1,298 Chinese siblings were surveyed using questionnaires, and structural equation modelling was used to test the mediation effect. Results: Contact frequencies of TD siblings were significantly affected by discretionary motivation, obligatory motivation, and stigma experiences. The findings supported the mediating effect of obligatory motivation in the relationship between affiliated stigma and contact frequency. Conclusion: This study is among the first to examine whether the relational motivation of TD siblings predicts their contact frequency within their relationships with adult siblings with ID. We found that both types of relational motivations of TD siblings positively predicted contact behavior.