Psyllium is the common used name for the plant genus Plantago, and seeds of Plantago are used commercially for the production of mucilage, a polysaccharide. Psyllium has many bioactivities, including immune-regulation, lowering blood sugar, plasma lipids and serum cholesterol, and it can be used as a drug carrier for targetable devices for therapeutic agents or controlled release devices. Its function on improving intestinal track health is widely accepted; psyllium increases faecal moisture and the pH value of defecation, and improves short-chain fatty acid production in the colon. These bioactivities – especially intestinal track health improvement – are considered to be related to the high viscosity and gelling properties of psyllium. The aim of this article is to summarize the physicochemical properties, structural characteristics and biological activity of psyllium.