Oxalic acid is an organic substance, chemical form HCO It is a metabolite of living organisms. It is a moderately strong acid. It is widely distributed in plants, animals, and fungi, and performs different functions in different living organisms. Studies have found that more than 100 kinds of plants are rich in oxalic acid, especially spinach, amaranth, beet, purslane, taro, sweet potato and rhubarb and other plants have the highest content. Because oxalic acid can reduce the bioavailability of mineral elements, it is easy to form calcium oxalate with calcium ions in the human body and lead to kidney stones, so oxalic acid is often considered as an antagonist for the absorption and utilization of mineral elements. Its anhydride is carbon sesquioxide.