We prepared a nanofibrous adsorbent for anionic dye removal from aqueous solution by electrospinning a modified polyethylenimine (m-PEI) and polyvinylidene fluoride (PVDF) blend. The electrospun nanofibrous adsorbent was confirmed to be a nanoscale, porous material with a positively charged surface; these characteristics are quite beneficial for anionic contaminant adsorption. Experimental adsorption of an anionic dye, methyl orange (MO), demonstrates that this adsorbent can rapidly remove MO from aqueous solution; its maximum adsorption capacity was 633.3 mg g(-1), which is much higher than that of previously reported adsorbents. After immersion in a basic solution, the adsorbent was well regenerated and showed good recyclability. The adsorption performance of the nanofibrous adsorbent is greatly influenced by the temperature, initial MO concentration, and pH of the solution. We further found that MO adsorption onto the adsorbent can be described well by the pseudo-second-order kinetic model and Langmuir isotherm model. Weber-Morris plots suggested that the adsorption of MO onto the nanofibrous mat was affected by at least film diffusion and intraparticle diffusion. This study indicates that nanofibrous PEI composite mats could be promising for treatment of wastewater containing anionic dye.