A new sensor containing MgFe₂O₄ nanoparticles in modified multiwall carbon nanotubes (MgFe₂O₄-MWCNTs) was prepared, and its electrochemical behavior was investigated. MgFe₂O₄-MWCNTs were used as a voltammetric sensor for the electrocatalytic determination of ciprofloxacin. The synthesized materials were characterized by different methods such as transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry, and electrochemical impedance spectroscopy. The MgFe₂O₄-MWCNTs electrode showed an oxidation peak potential at around 250 mV. The immobilized composite films facilitate interfacial electron transfer and electrocatalytic activity on the oxidation of ciprofloxacin. The oxidation peak current was dependent on the ciprofloxacin concentration, which was linear over the range of 0.10 – 1000 μmol L⁻¹ with a detection limit and quantification limit of 0.01 and 0.08 μmol L⁻¹, respectively. The relative standard deviation for the determination of 1.0 μmol L⁻¹ ciprofloxacin was 1.1%. The repeatability of the sensor was investigated by preparing nine similar electrodes. The proposed sensor is a selective and fast tool for the determination of ciprofloxacin in tablet, plasma, and urine samples.