The polyacrylonitrile (PAN) fibers were modified with hydroxylamine and its mixture with hydrazine to prepared the amidoximated PAN fibers (denoted as AO-PAN) and mixing modified PAN fibers (denoted as M-PAN) respectively, and then both of which were reacted with Fe 3+ ions to form two modified PAN fiber-Fe complexes (denoted as Fe-AO-PAN for AO-PAN and Fe-M-PAN for M-PAN). Their mechanical properties were evaluated and compared with respect to the breaking strength and elongation at break in both dry and wet conditions, and two important effecting factors including weight gain rate of the PAN fiber after modification and Fe content remained in the PAN fiber were investigated. Besides, thermal behavior of the modified PAN fibers and their Fe complexes was also examined by DSC and DMA methods. The results indicated that higher weight gain rate imparts the reduced breaking strength to two modified PAN fibers, and which is found to be further lower in wet state. The mechanical properties of the modified PAN fibers-Fe complexes, especially Fe-AO-PAN varied with Fe content (C Fe-PAN ). Moreover, two critical C Fe-PAN values are observed to be 79.75 mg/g for Fe-AO-PAN and 28.35 mg/g for Fe-M-PAN, respectively, at which they show a minimum values of breaking strength and elongation at break. Also, Fe-AO-PAN is much higher than Fe-M-PAN in terms of the critical C Fe-PAN value, which is mainly attributed to the difference in molecular structure between them. Thermal behavior of the modified PAN fibers and their Fe complexes is also greatly affected by their modification methods.