Multi-walled carbon nanotubes decorated with Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs/MWCNTs) were prepared and used to fabricate an electrochemical sensor for the determination of enrofloxacin. The electrochemical response of the carbon paste electrode (CPE) modified with Fe 3 O 4 NPs/MWCNTs towards enrofloxacin was investigated by cyclic voltammetry and differential pulse voltammetry. The results indicated a remarkable growth in the oxidation peak current together with negative shift in the oxidation peak potential for enrofloxacin, in comparison to both the unmodified CPE and the CPE modified with MWCNTs (MWCNT/CPE). The prepared sensor displayed a rapid and sensitive response towards enrofloxacin, which was attributed to the synergetic electrocatalytic effect of Fe 3 O 4 NPs and MWCNTs. The sensitivity enhancement with nearly three orders of magnitude (0.3-100 μM) was gained, compared with the MWCNT/CPE, with a detection limit of 0.09 µM (S/N = 3). The proposed method was successfully applied for the highly sensitive determination of trace amounts of enrofloxacin in cow's milk, egg, honey and chicken samples.