A nanosensor was introduced for a sensitive determination of methyldopa using multiwall carbon nanotubes (MWCNTs) decorated with ferrite nickel nanoparticles (NiFe2O4) on a glassy carbon electrode. The electrochemical activity of the modified electrode for the determination of methyldopa was investigated using differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The results showed that the modified electrode exhibits synergistic activity to the oxidation of methyldopa. The influence of several parameters that affect the response of the modified electrode was studied. A wide linear dynamic range of 0.5 to 900 μmol L−1methyldopa with a detection limit of 0.08 μmol L−1 was achieved using differential pulse voltammetry. The interference of foreign substances on the selectivity of the electrochemical sensor was evaluated. Finally, the proposed method was successfully applied for the determination of methyldopa in real samples such as human urine, tablet, and plasma with satisfactory results.