Rayon-based activated carbon fiber (ACF) was modified with several methods: acetonitrile thermal chemical vapor deposition at 800 °C (8AN) to dope nitrogen element on carbon surface, heat treatment at 950 °C (9.5HT) to convert doped nitrogen species into quaternary nitrogen (N-Q) and steam activation at 800 °C (8ST) to additionally develop pore structure. The modified samples were evaluated as adsorbents for the removal of nitrate from NaNO3 aqueous solution at equilibrium solution pH (pHe) around 3.0. Sequential modification of ACF with 8AN, 9.5HT and 8ST achieved the greatest adsorption capacity at 0.7 mmol/g in all prepared samples. The modified adsorbent was probably included in the greatest group in nitrogen-doped carbonaceous adsorbents for nitrate removal. To inspect the high adsorption capacity, specific surface area, elemental analysis and X-ray photoelectron spectroscopy measurements were conducted comparing with the other prepared adsorbents. Based on the data analysis, some specific surface area and N-Q might play an important role in the adsorptive removal of nitrate.