Grounded in attachment theory, the present study aimed to examine the predictive effects of deceased-specific attachment styles (anxious and avoidant) on grief and to test the mediating roles of two dimensions of unfinished business, namely unfulfilled wishes and unresolved conflicts. Using a two-wave longitudinal design, we conducted a 3-month follow-up survey (T1: October 2024; T2: January 2025) among Chinese adults who experienced bereavement within the past five years. Participants completed the Experiences in Close Relationships—Relationship Structures questionnaire at T1 and the Unfinished Business in Bereavement Scale and the International Prolonged Grief Disorder Scale at both T1 and T2. A total of 206 participants (Mage = 25.07 years; 51.94% women) completed both assessments. After controlling for T1 grief, demographic- and loss-related covariates, T1 deceased-specific attachment anxiety and attachment avoidance did not directly predict T2 grief. However, T1 deceased-specific attachment avoidance significantly negatively predicted T2 unfulfilled wishes, and both unfulfilled wishes and unresolved conflicts at T2 significantly positively predicted T2 grief. Furthermore, T2 unfulfilled wishes significantly mediated the relationship between T1 deceased-specific attachment avoidance and T2 grief. Thus, directly targeting unfinished business may serve as a more efficient and specific clinical strategy than broad attachment-focused interventions.