The present study designed an electro-chemical instrument with high sensitivity and selectivity on the basis of a SPE modified with La+3/Co3O4 nano-cubes in order to analyze vitamin B9. It was confirmed that this sensor possesses very good electron-moderating behaviors to oxidize vitamin B9 in a 0.1 M phosphate buffer solution (PBS) (pH=7.0). In addition, according to optimal conditions (pH=7.0), a potential around 110 mV less positive than the one in the un-modified electrodes is required for vitamin B9 oxidation at this electrode surface. This technique limit of determination for vitamin B9 has been estimated to be 0.3 μM (S/N = 3). Responses have been linear in concentrations range between 1.0 and 600.0 μM. The modified electrode has been applied to detect vitamin B9 in real specimens, which was accompanied by acceptable outputs. Experiments showed that La+3/Co3O4 nano-cubes will be valuable electrode materials providing a high ratio of surface to volume that enhances sensitivity. The study introduces a novel sensor with simpleness, quickness, sensitivity, and affordability features to quantify vitamin B9.