Eco-friendly chemical oxygen demand (COD) sensors are highly desired with respect to the importance of COD determination in environmental protection. In this work, a new FTO/TiO₂/PbO₂ (FTO = fluorine-doped tin oxide) electrode was fabricated with a two-step method and used as an eco-friendly electrochemical COD sensor. The interlayer TiO₂ was employed to strengthen the adhesion of PbO₂ on the FTO substrates by providing a large TiO₂/PbO₂ interface area. The effects of the factors including applied potential, supporting electrolyte concentration and stirring speed on the sensing performance were investigated. Under the optimized conditions, linear responses to the COD of water with different COD sources were achieved, and a linear range from 5 to 120 mg/L was obtained in the case of sucrose as the COD source. The relative standard deviations (RSD) were determined to be less than 9% for the glucose solutions with the COD of 7.5, 12.5 and 17.5 mg/L. For real sample analysis, the obtained results were comparable with those measured with the conventional dichromate method, with a relative error less than 11%.