3, 4-dihydroxybenzoic acid, also known as protocatechuic acid, is a phenolic acid compound, is also a relatively simple phenolic acid, molecular formula C7H6O4, molecular weight 154.12, CAS number 99-50-3, EINECS number 202-760-0.

3,4-dihydroxybenzoic acid is naturally found in nuts, fruits, vegetables, tea, brown rice, hibiscus flower, hory and some Chinese herbal medicines. It can be used as a precursor for the synthesis of many complex molecules, such as vanillin and anthocyanin 3-O-β -D-glucoside. As 3,4-dihydroxybenzoic acid has antibacterial, anti-inflammatory, antioxidant and other biological activities on different molecular targets, as well as potential chemical protection, it has a certain inhibitory effect on chemical carcinogens, apoptosis and proliferation in vitro. Therefore, in the medical field, 3,4-dihydroxybenzoic acid is often used in the treatment of acute pancreatitis, acute pyelonephritis, dysentery, burn, pneumonia in children and some ulcer diseases.