Abstract: Electrochemical behaviour of nitrobenzene at the GCE modified with carboxylated multwall carbon nanotubes was studied and its mechanism of electrochemical reduction was discussed.It was found that in 0.2 mol·L-1 H2SO4 solution,the reduction of nitrobenzene at the modified electrode was remarkably catalyzed,showing a positive shift of the reductive peak potential of 90 mV as from -0.44 V (at the bare GCE) to -0.35 V (at the modified electrode of CMWCNT′s/GCE) and a negative shift of the oxidative peak potential of 50 mV as from 0.35 V (at the bare GCE) to 0.30 V (at the modified GCE).Cyclic voltammetric determination of nitrobenzene was performed in the linearity range of 5.0×10-7-4.2×10-5mol·L-1 in respective to the values of reductive peak current.Value of detection limt (3S/N) found was 8.2×10-8mol·L-1.Using the sample of lake water as matrix,test for recovery was made by standard addition method,and values of recovery found were in the range of 98.3%-100.6%.