In this study, fabrication, characterization, and adsorption properties of alginate (Alg)-based nanofibrous membrane were investigated for two categories of anionic (AR14) and cationic (BB41) dyes. Three optimization steps were performed to achieve the membrane enjoying desirable morphology, highest Alg content, and lowest possible nanofiber diameter. Consequently, Alg/poly(ethylene oxide) nanofibers with the 80:20 ratio and mean diameter of 93 nm were produced. A novel method was applied as spraying the cross-linking solution to diminish the solubility of the nanofibers in aqueous environments. The effect of solution pH, contact time, membrane dosage, and dye concentration on the adsorption performance was evaluated. The results showed that the produced membrane has an obvious pH dependency in which the maximum adsorption capacity at the solution pH of 1 and 9 were 93% and 71% for AR14 and BB41, respectively. The present work revealed that the Alg-based nanofibrous membranes have a great potential to remove both anionic and cationic dyes from aqueous solutions.