Monitoring vitamins is essential as they play a significant role in human metabolisms. Folic acid (FA), one type of vitamin B, is responsible for various functions, including new red blood cells, synthesis, and repair of DNA. Therefore, the detection of FA is crucial. Here, we report poly (3, 4-ethylenedioxythiophene) (PEDOT) and cadmium oxide (CdO) (PEDOT-CdO) composite for the effective sensing of FA. The PEDOT nanospheres were prepared by the wet chemical method, and CdO nanorods were synthesized using the hydrothermal technique. The sulfur groups in PEDOT connected with Cd2+ ions in CdO nanoparticles enriched their electrostatic interaction developing a robust and straightforward electrochemical FA sensor. The as-prepared PEDOT-CdO biosensor exhibited good electrocatalytic activity towards selective determination of FA in the linear range of 40 nM-1 mM with a lower detection limit of 8.4 nM. In addition, the investigation of cytotoxic nature against human breast cancer cell lines (MCF-7) reveals that, the reported composite induces apoptotic cell death and can be used as an anticancer agent. The proposed biosensor can be used for device fabrication in sensor applications as well as a vector for targeted drug delivery for cancer cell diagnosis.