In this paper, poly(vinyl alcohol) (PVA) nanofiber was prepared and modified by diethylenetriamine (DETA) and ethylenediamine (EDA) in the presence of glutaraldehyde (GA). Dye removal ability of the modified nanofiber (PVA/DETA/EDA/GA) as a nanoadsorbent from water was studied. Fourier transform Infrared (FTIR) and scanning electron microscopy (SEM) were used to investigate the characteristics of the modified nanofiber. Direct Red 23 (DR23) and Direct Blue (DB78) were used. The effect of operational parameters such as pH, initial dye concentration, contact time, temperature and adsorbent dosage on dye removal was studied. The dye adsorption isotherms, kinetics and thermodynamics were investigated. The maximum dye adsorption capacity of the modified nanofiber was 370 and 400 mg/g for DR23 and DB78, respectively. Four isotherms, the Langmuir, the Freundlich, Tempkin and a modified Langmuir-Freundlich model were used. Dye adsorption on the modified nanofiber followed the Langmuir isotherm and pseudo-second kinetic order. Thermodynamic data showed that dye removal was a spontaneous, endothermic and physisorption process.