In this paper the electrochemical behaviour of carbon paste electrodes, which were previously modified with different amounts of ternary sulphides (three different sulphides), has been tested for the purpose of L-cysteine electrochemical determination. Electrochemical processes spotted on the electrodes that have been modified this way indicate the possibility of indirect L-cysteine determination. This method is based on the formation of the stable complexes of L-cysteine and ternary sulphides’ metal ions. The measurements have been conducted at two pH values (pH 5 and 7) and subsequently the pH 5 has been chosen as the optimum. The electrochemical determination of L-cysteine has been carried out through the usage of squarewave voltammetry method (SWV). The best results were acquired by using the electrode that had been modified with 5% of the material which consisted of various ternary sulphides with a general formula Cu X Ag y S z as well as of elementary silver. In the paper, the effect of various parameters on the electroanalytical signal has been shown, such as the amount of electroactive material, sweep speed, different electrical contacts, frequency, anode and cathode squarewave voltammetry (SWV). This method has indicated that the determination processes are controlled by diffusion and adsorption. The electrode mentioned above has shown the satisfactory sensibility of the anode signal at 10 Hz of -20 μA μmol -1 dm 3 with the linear range from 0,1 to 1 μmol dm -3 . The detection limit, which has been determined with 3σ method, is 0,0025 μmol dm -3 . Also, in this paper the other occurrences, which could be perceived after changing the parameters, have been studied.