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A series of polyimide/polyacrylonitrile (PI/PAN) blend fibers with different PAN weight ratios were prepared through a two-step wet-spinning method and stabilization process and then were carbonized at 1500°C under high-purity nitrogen atmosphere, yielding in PI/PAN-derived carbon fibers. The effects of PAN content on the structures of the PI/PAN blend fibers were systematically investigated. The elemental composition, aggregation structure, carbon yields, and electrical properties of the PI/PAN-derived carbon fibers were also analyzed. The imidization degree and molecular orientation of the PI/PAN blend fibers increased first and then decreased with increasing PAN content, which directly affect the aggregation structures and properties of the corresponding PI/PAN-derived carbon fibers. As a consequence, the carbon fibers derived from PI/PAN-35% exhibited perfect graphite structure with a planar spacing d002 of 0.349 nm, high carbon content of 97.14%, and low electrical resistivity of 1.89 × 10−5 Ω·m, attributing to the high degree of orientation along the fiber axis and low value of φa/φc in the PI/PAN blend fibers. [ABSTRACT FROM AUTHOR]