Impurities identification, synthesis and its control are the key factor for drug quality and specification. Impurity study enhances scope towards better production of drug molecules.New impurities 5-methoxy-1-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-2-((4-methoxy-3,5-dimethylpyridin-2-yl)methylthio)-1H---benzo[d]imidazole and 6-methoxy-1-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-2-((4-methoxy-3,5-dimethylpyri-din-2-yl)methylthio)-1H-benzo[d]imidazole have been identified, synthesized and analyzed in ufiprazole (5-methoxy-2-((4-methoxy-3,5-dimethylpyridin-2-yl)methylthio)-1H-benzo[d]imidazole). Both dimer impurities were isolated with HPLC purity more than 98% and characterizedby IR, 1H-NMR, 13C-NMR and LCMS.