Abstarct: Sulfonamides are antibacterial agents that contain sulfur and amine groups in their molecular structure. These medications are widely used and applied in curing infection and bacteria diseases. Beside their effective therapeutic role their residue may cause toxicity in environment and can make disease if entered in living creature's bodies. Today, having a device which is able to measure these medications simple and cheap in trace analysis is important. As these materials are electroactive, their behavior and concentration can be monitored by designed electrodes (sensors). In this work we studied the electrochemical behavior of some sulfonamides derivatives called sulfadiazine (SDZ), sulfathiazole (STZ), sulfaquinoxaline (SQX), sulfacetamide (SAA) and sulfasalazine (SSZ) on modified carbon paste electrodes by cyclic voltammetry (CV). In order to optimize the electrochemical behavior of these medications on surface of electrodes some modifiers including nano-silica ionic liquid, lanthanide nano-oxides, carbon nanomaterials and carbon-lanthanide nano-composites were used. Among modified carbon paste electrodes for studied sulfonamides, the electrode which contained 5% of reduced graphene oxide (RGO) decorated CeO2 nano-composite showed a significant increase in current in comparison with bare electrode toward sulfadiazine (SDZ). Decoration of cerium oxide NPs on RGO prevented cerium oxide NPs from aggregation and RGO nano-sheets from restacking. A fast Fourier transform square wave voltammetry (FFTSWV) was applied in order to reveal the measurement applicability of the proposed electrode for SDZ determination. Calibration curve was obtained for SDZ had two linear ranges from 3 to 10 µM (R2=0.9956) and from 30 to 1000 µM for sulfadiazine (R2=0.9948). LOD with the value of 0.17 µM and LOQ with the value of 0.58 µM were calculated. SDZ measurement in some pharmaceutical formulations was done by the proposed method and the nano-composite modified electrode. By the relative error value of 4.6% results were obtained.