In the present study, thiol β-cyclodextrin (SH-CD) and ethylenediamine β-cyclodextrin (NH₂-β-CD) were simultaneously grafted on the same interface of an Au NP deposited carboxyl SiC (Au@CSiC) nanocomposite. An electrochemical sensor for the simultaneous determination of nitrophenol isomers (o-nitrophenol, o-NP; p-nitrophenol, p-NP) using SH-CD and NH₂-β-CD functionalized Au@SiC (Au@CSiC-SH/NH₂-CD) nanocomposite was successfully constructed. Differential pulse voltammetry was used to quantify o-NP and p-NP within the concentration range of 0.01–150 μM under the optimal conditions. The detection limit (S/N = 3) of the sensor was 0.019 and 0.023 μM for o-NP and p-NP, respectively, indicating a low detection limit. Interference study results demonstrated that the sensor was not affected in the presence of similar aromatic compounds during the determination of NP isomers, showing high selectivity. The proposed electrochemical sensing platform was successfully used to determine NP isomers in tap water. The low detection limit and high selectivity of the proposed electrochemical sensor were caused by the high surface area, the excellent conductivity, and the more recognized (enriched) NP isomer molecules by SH-β-CD and NH₂-β-CD of the Au@CSiC-SH/NH₂-CD nanocomposite.