Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical behavior of ascorbic acid at a carbon paste electrode modified with 2,2'-(1,8-octanediylbisnitriloethylidine)-bis-hydroquinone (1,8-OBNEBHQ). The modified carbon paste electrode showed high electrocatalytic activity toward ascorbic acid; the current was enhanced significantly relative to the situation prevailing when an unmodified carbon paste electrode was used. The electrocatalytic process was highly dependent on the pH of the supporting electrolyte. The apparent charge transfer rate constant, k(s), and transfer coefficient, a, for electron transfer between 1,8-OBNEBHQ and carbon paste electrode were calculated as 20.2 +/- 0.5 s(-1) and 0.47, respectively. Using differential pulse voltammetry, the calibration curves for AA were obtained over the range of 5-30 and 40-1,500 mu M, respectively. The detection limit (k sigma, k = 2) was 0.6 mu M. With good selectivity and sensitivity, the present method provides a simple method for selective detection of ascorbic acid in biological samples.