Cobalt-Platinum bimetal nanoparticles (CoPtNPs) were electrodeposited on bare Pt electrode. A highly sensitive amperometric sensor-based on CoPtNPs/Pt modified electrode was constructed to determine ascorbic acid (AA). The Co-Pt nanoparticles were characterized by scanning electron microscopy (SEM) andcyclic voltammetry (CV). Due to the synergistic effects of Co-Pt nanoparticles, the electrocatalytic activity of modified electrode showed a significant enhancement toward the oxidation of AA compared to Co/Pt and bare Pt electrodes in alkaline medium. The electrocatalytic activity of CoPtNPs/Pt was studied as a function of Co:Pt molar ratio in the deposition bath. The analytical performance of the proposed sensor has been investigated by chronoamperometry method under the optimized conditions. This sensor showed a linear response to AAconcentration range from 10 µM to 0.5 mM with a detection limit of 0.37 µM (S/N = 3), a high sensitivity of 103 µA mM_-1 , and a fast response time. In addition, the reproducibility, selectivity and applicability of this sensor were assessed with satisfactory results