Background Openness to experience is positively associated with emotion recognition ability in middle-aged and older adults, yet the underlying neurocognitive mechanisms remain unclear. Methods Using a serial mediation model, the present study examined the neurocognitive pathways through which openness to experience influences emotion recognition accuracy and processing speed via hippocampal volume and fluid intelligence in 912 middle-aged and older adults aged 36–100 years, with age, sex, intracranial volume, and acquisition site included as covariates. Results Openness had a significant direct positive effect on emotion recognition accuracy. The indirect effect of openness through fluid intelligence was significant and accounted for 85.4% of the total indirect effect. The serial indirect pathway through hippocampal volume followed by fluid intelligence was also significant. The same serial pathway was replicated for processing speed. Notably, hippocampal volume additionally showed a significant direct path to processing speed, a finding absent in the accuracy model. Conclusion These findings reveal a serial neurocognitive pathway from personality trait to brain structure, through domain-general cognitive resources, and ultimately to social cognitive performance. Fluid intelligence appears to be the primary neurocognitive mechanism linking openness-related hippocampal preservation to emotion recognition performance, and the significant serial pathway further suggests that hippocampal volume may not directly affect emotion recognition, but rather exerts its effect indirectly through fluid intelligence. The results suggest that individuals with higher openness showed larger hippocampal volume, which in turn was associated with better fluid intelligence and greater emotion recognition accuracy. The replication of this pathway for processing speed, together with a novel direct hippocampal contribution to response speed, provides converging support for the robustness of the proposed neurocognitive mechanism across complementary performance indicators.