Abstract: Electrochemical behavior of cytochrome c immobilized on the modified electrode of L-cystein/Au(abbreviated as Cyt.c/L-Cys/Au) was studied by cyclic voltammetry and alternating impedance,and the modified electrode was characterized by electrochemical methods and UV-VIS spectrophotometry.As shown by experimental results,cytochrome c,immobilized electrostatically on the L-cysteine/Au electrode,behaved to keep its biological and electrochemical activity in a good state.The modified electrode Cyt.c/L-Cys/Au was used as working electrode in the voltammetric determination of nitrite radical,and linear relationship between the values of response peak current(Ip) and concentration of NO-2 ion was obtained in the range from 5.0×10-6 to 4.5×10-4mol·L-1 in respective to the linear regression equation of Ip=0.031 c+8.165×10-6(r=0.999 5).Detection limit(S/N=3) of the method was found to be 1.5×10-7mol·L-1.Simulated samples and samples of pickles were analyzed by the proposed method,giving values of recovery in the range of 89.0%-116.0%.