A new tin doped ceria nanoparticle modified glassy carbon paste electrode (Sn–CeO₂NPs/GCPE) was fabricated for the determination of the anticancer drug dacarbazine (DTIC). The Sn–CeO₂ nanoparticles with Sn concentrations from 0 to 10 wt% were synthesized by sol gel method. Sn doped CeO₂ nanoparticles were characterized by X-ray diffraction, energy-dispersed X-ray spectrometry (EDS) and transmission electron microscopy (TEM). Cyclic voltammetry (CV) and square wave voltammetry (SWV) were applied to investigate the unique properties of the Sn–CeO₂NPs/GCPE. The modified electrode showed an excellent character for electrocatalytic oxidization of DTIC, while the bare GCPE electrode only gave a small oxidation peak. The fabricated sensor showed an excellent anti-interference ability against electroactive species and metal ions. This modified electrode was used as a sensor for determination of DTIC in human biological fluids and in pharmaceutical samples with satisfactory results.