Magnetic Fe 3 O 4 nanoparticles functionalized multiwalled carbon nanotubes (nano-Fe 3 O 4 MWNTs) were prepared for electrochemical sensors. 2-amino-5-mercapto-1,3,4-thiadiazole was used as a connecter to form a network that connected nano-Fe 3 O 4 MWNTs to the Au electrode surface. Modified process of the electrode was studied with SEM, TEM and cyclic voltammetry. Cyclic voltammetry and amperometric i-t curve were used to investigate characteristics of the obtained electrode. The sensor has been successfully used on the direct detection of catechol and showed excellent performances. The linear regression equation was I pa (mA) ¼ 0.07763 þ 0.16739 C (mmol/L); R ¼ 0.9993 and the detection limit was 5.38 Â 10 À8 mol/L. The modified electrode showed good reproducibility and stability.