Dyes are a severe threat for the environment and health. Therefore, the removal of dyes is a significant consideration in the wastewater purification. In textile industries, the most widely used dyes are reactive dyes due to their ease of use. Among reactive dyes, reactive black 5 has been the most utilized dye with 50% of the total reactive dye demand. In this study, polyacrylonitrile-co-poly(2-ethylhexylacrylate) copolymer (PAN-co-P2EHA) membranes with various acrylonitrile/2-ethylhexylacrylate (AN/2EHA) ratios were synthesized and tested for the removal of reactive black 5 dye from wastewater with the aid of filtration method. The copolymer with a AN/2EHA ratio of 92/8 demonstrated the best filtration performance. Also, it was blended with different polyaniline (PANI) loadings in order to functionalize pores. Moreover, effects of permeate pH and concentration were also analyzed. It was observed that, after functionalization of pores, filtration performance became pH dependent and better results were observed at acidic medium. PAN(92)-co-P2EHA(8)/PANI(15) membrane having AN/2EHA molar ratio of 92/8 with 15 weight% PANI loading showed the best dye rejection performance at pH 2 by 99.5%, 98.4% and 90.5% for permeate concentrations of 100, 200 and 300 ppm, respectively.