Low-dimensional calcined (500.0 °C) erbium oxide–copper oxide doped nanomaterials (Er₂O₃/CuO) were synthesized in alkaline pH using a wet-chemical method. The optical, structural and morphological properties of an Er₂O₃/CuO nanomaterial were characterized in detail using FT-IR, PL, XRD, UV/vis techniques in addition to the FESEM and EDS analysis. A thin layer of Er₂O₃/CuO was fabricated on to the glassy carbon electrode (GCE) with conducting nafion binders for the development of a selective and sensitive 3-chlorophenol (3-CP) sensor. Electrochemical responses along with a higher sensitivity, large dynamic range, lower detection limit, and long-term stability towards 3-CP were found by an electrochemical I–V approach. It is an organized route for developing the chemical sensor based on a very low-dimensional Er₂O₃/CuO nanomaterial/GCE using electrochemical oxidation phenomena. This method could be a pioneer development in 3-CP sensor using co-doped nano-structural materials in the simple electrochemical method for the various phenolic sensor applications for environmental safety in broad scales.