Abstarct: In this thesis, glassy carbon electrode was modified with carmoisine and applied for the sensitive and selective voltammetric determination of thiouracil derivatives. The electrochemical behavior of catechol in the presence of thiouracil derivatives with cyclic and differential pulse voltammetry techniques in pH 3-9 was investigated at the surface of modified electrode. In this study, carmoisine as a modifier using cyclic voltammetry technique was at the surface of electrode stabilized. An ECE mechanism was proposed for the oxidation of thiouracil derivatives at the modified electrode surface. Chemical and Instrumental parameters were investigated and optimized for the determination of thiouracil derivatives. In this research, the modifying of electrode causes the separated of anodic peaks related to the catechol and product and the background current decreases in the potential of oxidation of the product anodic peak and of the anodic peak current of product was used to determination of thiouracil derivatives this causes improves the detection limit. The effect of various drugs, such as L-acetyl cysteine, captopril, L-glutathione on the electrochemical behavior of catechol was investigated in the optimum conditions. The results show the effect of thiouracil derivatives for improving the anodic peak current of catechol. The linear range for MTU, using differential pulse voltammetry, was from 0.06 to 2.00 μM with a detection limit of 0.05 μM. A linear range from 0.04 to 1.50 μM with a detection limit of 0.02 μM is obtained for the determination of 2TU. In addition, determination of the thiouracil derivatives was evaluated in real samples of human blood serum and water with differential pulse voltammetry.