Neoproterozoic mafic dyke swarms are key indicators for reconstructing the timing and dynamic processes of the Rodinia supercontinent breakup. Based on systematic analyses of zircon chronology, whole-rock geochemistry, and zircon Lu-Hf isotopes, this study investigates the petrogenesis and geodynamic setting of a newly discovered diabase dyke swarm in the Mianning area on the western Yangtze Block, South China. LA-ICP-MS zircon U-Pb dating reveals that the Mianning diabase crystallized at 835.8±4 Ma, indicating its formation during the Neoproterozoic. The diabase exhibits variable SiO₂ content (45.2% to 48.0%) and MgO (6.82% to 8.15%) contents, as well as Mg^# values (46~57), along with high Al₂O₃ (14.00%~15.75%) content. The studied rocks display relatively flat rare earth element (REE) distribution patterns, with enrichment in Rb, Ba, and K, and depletion in Nb, Ta, Sr, and P. The studied rocks exhibit enriched zircon Lu-Hf isotopes [εHf(t) = -2.2~1.6]. Petrogenetic analysis indicates that the Mianning diabase originated from low-degree partial melting of an enriched mantle wedge, with the mantle source having been modified by fluids derived from altered oceanic crust. The Neoproterozoic Mianning diabase on the western Yangtze Block formed in an extensional continental arc setting, implying that the western margin of the Yangtze Block may have been located at the periphery of the Rodinia supercontinent during the Neoproterozoic era.