NOVELTY - Production of buzolic acid (I) involves adding o-phenylenediamine (II) to xylene, heating, adding ethylacetoacetate (III), reacting, concentrating, adding non-polar solvent, crystallizing, filtering, adding obtained 1-isopropenyl-1,3-dihydro-2H-benzimidazol-2-one (IV) to polar solvent, heating, adding solution of 4-bromo-ethyl butyrate (V), reacting, cooling, adding inorganic alkali aqueous solution, saponifying, cooling reaction solution containing 4-(3-isopropenyl-2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)butanoic acid (VII), adding chemical acceptable acid, stirring, and reacting.    USE - Production of buzolic acid (claimed).    ADVANTAGE - The method enables economical production of buzolic acid with high yield and purity, under mild reaction conditions, by simple and environmentally-friendly process.    DETAILED DESCRIPTION - Production of buzolic acid of formula (I) involves adding o-phenylenediamine of formula (II) to xylene, heating, adding ethylacetoacetate of formula (III) for 2-5 hours, reacting resultant mixture at 120-150 degrees C for 1-5 hours, concentrating the reaction solution, adding non-polar solvent, crystallizing, filtering, adding obtained 1-isopropenyl-1,3-dihydro-2H-benzimidazol-2-one of formula (IV) to polar solvent, adding inorganic alkali, heating resultant mixture to 100-150 degrees C, adding solution of 4-bromo-ethyl butyrate of formula (V) for 2-20 hours, reacting for 0.5-8 hours, and cooling reaction solution containing ethyl 4-(3-isopropenyl-2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)butanoate of formula (VI), adding inorganic alkali aqueous solution, and saponifying, or cooling reaction solution containing compound (VI) to -5 degrees C to 15 degrees C, adding inorganic alkali aqueous solution, stirring for 0.5-3 hours and reacting at 20-40 degrees C for 3-8 hours, cooling reaction solution containing obtaining 4-(3-isopropenyl-2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)butanoic acid of formula (VII) to -10 degrees C to 25 degrees C, adding chemical acceptable acid, stirring for 0.5-3 hours, and reacting at 15-50 degrees C for 1-8 hours. The molar ratio of compound (II) and compound (III) is 1:1-1:5. The molar ratio of compound (IV) and 4-bromo-ethyl butyrate solution is 1:0.8-1:4.