Social support can promote posttraumatic growth (PTG) in the general trauma population. However, evidence on the reciprocal predictive relationship between social support and PTG is lacking, particularly among the bereaved. In this longitudinal study, we surveyed 181 adults who had lost first‐degree relatives within 1 year at three intervals, each 6 months apart. The study utilized The Scale of Social Support in Bereavement (SSB), which distinguishes four domains of social support for the bereaved: living support, economic support, grief processing and emotion restoration. Additionally, The Posttraumatic Growth Inventory (PTGI) was used to measure PTG. Random intercepts cross‐lagged panel model analyses revealed that social support and PTG were positively correlated at each time point at the within‐person level. Moreover, at the within‐person level, the total social support, as well as social support in the restoration‐oriented domains at Time 2, positively predicted PTG at Time 3, but this relationship was not observed for grief processing support. Additionally, PTG at Time 1 positively predicted the receipt of emotion restoration support at Time 2 at the within‐person level. The mutual influence between PTG and social support, as well as the differential relationship between types of support and PTG, enriches our understanding of ways to promote positive changes among the bereaved. The findings underscore the importance of restoration‐oriented social support for bereaved individuals in facilitating PTG.