NOVELTY - Preparing chenodeoxycholic acid in pig bile via esterification method, comprises e.g. (a) extracting the bilirubin and hyodeoxycholic, evaporating the mother liquor by rotary, adding 3-5 times of methanol, concentrated sulfuric acid (4%) to make it completely dissolve, standing for 10 minutes at normal temperature, adding sodium hydroxide for regulating pH to 6-7, standing for 2 hours, filtering, decompressing and concentrating at the pressure of 0.05-0.07 MPa and temperature of 40-45 degrees C, recycling the methanol to obtain ester paste.    USE - The method is useful for preparing chenodeoxycholic acid in pig bile (claimed), where the chenodeoxycholic acid is useful for treating cholesterol stones, as antibacterial, antiinflammatory, and antianaphylaxis, and for relieving heat, phlegm and asthma. No biological data given.    ADVANTAGE - The method is capable of safely preparing chenodeoxycholic acid in pig bile with high purity in large scale, simple and environmentally friendly manner.    DETAILED DESCRIPTION - Preparing chenodeoxycholic acid in pig bile via esterification method, comprises (a) extracting the bilirubin and hyodeoxycholic, evaporating the mother liquor by rotary, adding 3-5 times of methanol, concentrated sulfuric acid (4%) to make it completely dissolve, standing for 10 minutes at normal temperature, adding sodium hydroxide for regulating pH to 6-7, standing for 2 hours, filtering, decompressing and concentrating at the pressure of 0.05-0.07 MPa and temperature of 40-45 degrees C, recycling the methanol to obtain ester paste, (b) heating acetic anhydride, stirring and refluxing for 3 hours, standing, concentrating via reducing pressure of 0.08-0.1 Mpa at 90-95 degrees C, recycling the acetic anhydride and obtaining acylated paste, (c) adding the acylated paste to petroleum ether, heating, stirring and refluxing, standing for an hour, removing the lower water layer, washing the petroleum ether layer with water until the pH value of 5-7 at 50 degrees C for insulating and heating at 30 degrees C, filtering, decompressing and condensing at the pressure of 0.06-0.08 Mpa and temperature of 70-80 degrees C, recovering petroleum ether, to obtain the extracting paste, (d) adding ethanol (90-95%) to the petroleum ether paste, statically crystallizing, filtering, vacuum drying at below 60 degrees C, to obtain the primary crystal, (e) adding the petroleum ether to the primary crystal, heating to make it completely dissolve, stewing and cooling crystalline, filtering and drying, to obtain secondary crystallization, (f) weighing and drying the crystal and adding sodium hydroxide, washing with purified water, heating, saponification the mixture, cooling to room temperature, standing and layering it down layer, adding little purified water to dissolve and hydrochloric acid for adjusting pH value to 4-5, filtering to obtain crude product of chenodeoxycholic acid, and (g) adding acid to ethyl acetate and active carbon (5-10%) to the crude product, heating and refluxing for 30-60 minutes, filtering, washing into neutrality by water, decompressing and concentrating at the pressure of 0.04-0.06 MPa and temperature of 45-50 degrees C, recycling ethyl acetate to 1/8-1/4 of the original volume, cooling to room temperature, statically crystallizing, filtering, to obtain the catalpol, placing the crystal into a vacuum drying box to dry at 60 degrees C, to obtain refined chenodeoxycholic acid.