Sulfasalazine is a disease-modifying antirheumatic drug and is used in the treatment of rheumatoid arthritis, ankylosing spondylitis, juvenile arthritis, Chron's disease and ulcerative colitis. It has anti-inflammatory and antibacterial characteristics. In this paper, effect of the modification of the surface of glassy carbon electrode on the voltammetric response of sulfasalazine due to reduction of the azo-link was studied by cyclic voltammetry. Studied modifications of the surface were electrode with graphen, carbon nanotubes, bismuth nanoparticles and nanocomposite of bismuth nanoparticles and carbon nanotubes. The highest current peak was recorded on the surface modified with combination of nanomaterials, bismuth nanoparticles and carbon nanotubes at potential of -0.2 V. Then, the selectivity of the method was investigated by monitoring the influence of the interference of other molecules to the peak current of sulfasalazine reduction by square wave voltammetry. The investigated molecules were inorganic molecules such as KNO3, ZnSO4, Na2CO3, KH2PO4, CuSO4, MgSO4, NaCl and FeCl3, organic molecules such as glucose, lactose, folic acid, ascorbic acid, dopamine and citric acid, and interferences of drugs mesalazine, olsalazine and sulfadiazine. The electroanalytical method developed on the modified surface of electrode by the synergistics effect of bismuth nanoparticles and carbon nanotubes showed excellent selectivity and potential for voltammetric determination of sulfasalazine in biological fluids.