Ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was used to fabricate a new ionic liquid/carbon paste electrode (IL/CPE). The general behavior of this electrode was characterized by electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy. Results showed that the IL plays an important role in improving the conductivity, reversibility, and electron transfer rate of the electrode. Nickel-modified ionic liquid/carbon paste electrode (Ni/IL/CPE) was also constructed by immersion of the IL/CPE in 1.0 M nickel sulfate solution. IL showed significant effect on the accumulation of nickel species on the surface of the electrode. The Ni/IL/CPE was applied successfully to highly efficient (current density of 16.5 mA cm(-2)) electrocatalytic oxidation of formaldehyde in alkaline medium. Cyclic voltammetry and chronoamperometry techniques indicated that this electrode displays a considerable electrocatalytic activity toward the oxidation of formaldehyde. The effects of different scan rates and formaldehyde concentrations on the electrocatalytic activity of this modified electrode were investigated. Finally, the rate constant for chemical reaction between formaldehyde and redox sites of the electrode was calculated.