Protocatechuic acid (3,4-dihydroxybenzoic acid, PCA) is a simple phenolic acid. It is found in a large variety of edible plants and possesses various pharmacological activities. This bioactive compound is famous for its biological properties and pharmacological activities such as: antioxidant, antibacterial, anticancer, antiulcer, antidiabetic, antiaging, antifibrotic, antiviral, anti-inflammatory, analgesic, antiatherosclerotic, cardiac, hepatoprotective, neurological and nephroprotective. The neuroprotective effects of PCA, extracted from Alpinia oxyphylla, on H2O2 resulted in apoptosis and oxidative stress in cultured PC12 cells. Apoptotic cell death by H2O2 was dose-dependent. Enhanced effect of PCA on protecting PC12 cells against apoptosis, augmented glutathione (GSH) level and an increase in catalytic activity was investigated by flow cytometric analysis. In cytotoxic assays, PCA causes cell death in HepG2 cancerous cell line of liver showing that PCA stimulates the c-Jun N-terminal kinase (JNK) and p38 subgroups of the mitogen-activated protein kinase (MAPK) family. Treatment with PCA decreased OVA-induced airway hyper-responsiveness to inhaled methacholine. Cell inflammation and mucus hypersecretion was also decreased by PCA. Thus, PCA can be useful for treating asthma. Experimental studies strongly support the role of protocatechuic acid in the prevention of neurodegenerative processes, including Alzheimer's and Parkinson's diseases, due to its favorable influence on processes underlying cognitive and behavioral impairment, namely accumulation of the β-amyloid plaques in brain tissues, hyperphosphorylation of tau protein in neurons, excessive formation of reactive oxygen species and neuroinflammation.