Polymers of Intrinsic Microporosity (PIM-1) is a promising material for adsorption and separation applications. While PIM-1 displays high affinity for neutral species, it shows lack of interaction with charged molecules in an aqueous system due to non-polar nature of it. Functionalization of PIM-1 provides an advantage of tailoring the interaction ability as well as the adsorption performance of PIM-1 towards target pollutants. In this study, electrospun Polymer of Intrinsic Microporosity (PIM-1) fibrous membrane (PIM-FM) was reacted with borane dimethyl sulfide complex to obtain amine modified PIM-1 fibrous membrane (AM-PIM-FM). Furthermore, PIM-1 film, which is referred as PIM-1 dense membrane (PIM-DM), was also modified under the same conditions as a control material. Structural analyses have confirmed that nitrile groups of PIM-1 have been fully converted to amine group as a result of the reduction reaction. Average fiber diameter of parent PIM-1 fibers was found 2.3 ± 0.3 μm, and it remained almost the same after the amine modification. In addition, no physical damage has been observed on fiber structure based on the SEM analysis. Both amine modified PIM-1 dense and fibrous membranes became insoluble in common organic solvents. Before the modification, water contact angle of PIM-FM was 138 ± 2° which also remained almost the same after the modification, showing water contact angle of 131 ± 8°. The insolubility along with amine functionality make membranes promising materials for adsorption of anionic dyes from wastewater. Here, dye (i.e. Methyl Orange) removal ability of AM-PIM-FM from an aqueous system was investigated and compared with parent PIM-1 (PIM-FM) as well as dense membrane form (AM-PIM-DM). AM-PIM-FM shows extremely higher adsorption capacity than that of PIM-FM and AM-PIM-DM. The maximum adsorption capacity of AM-PIM-FM was found 312.5 mg g−1 for Methyl Orange. Langmuir isotherm model was found more favorable for the adsorption. AM-PIM-FM was employed effectively in continuous adsorption/desorption studies for several times without having any damage on fiber morphology using batch adsorption process. Furthermore, AM-PIM-FM was successfully used as a molecular filter for the removal of methyl orange from an aqueous system. The results indicate that AM-PIM-FM could be a promising adsorbent for removal of anionic molecules from an aqueous system.