Gallic acid (GA), also known as 3,4,5-trihydroxybenzoic acid, is a natural secondary metabolite and widely isolated from various fruits, plants and nuts. In recent years, GA has received increasing attention for its powerful anti-inflammatory properties. The purpose of this review is to clearly illuminate the pharmacological activities and related molecular mechanisms of GA in inflammatory diseases. After consulting a large number of literatures, we made a comprehensive exposition on the chemical characteristics, plant origins, pharmacokinetics and toxicity of GA, especially its pharmacological activities and mechanisms of action. Although the plant source of GA is very rich, its lower extraction rate limits the application of GA in development. It is worth mentioning that GA can not only be separated from many plants, but also be produced in large quantities through biological and chemical synthesis. According to pharmacokinetic studies, the absorption and elimination of GA after oral administration are fast, while the structural optimization or dosage form adjustment of GA is beneficial to increase its bioavailability. Promisingly, toxicity studies have shown that GA scarcely has obvious toxicity or side effects in a variety of animal experiments and clinical trials. The results show that the anti-inflammatory mechanisms of GA mainly involved MAPK and NF-κB signaling pathways. It thus weakens the inflammatory response by reducing the release of inflammatory cytokines, chemokines, adhesion molecule and cell infiltration. Due to its excellent pharmacological activities, GA is expected to be a potential candidate for the treatment of various inflammation-related diseases. This paper will provide theoretical basis for the clinical application of GA and guide the future research and medicinal development of GA.