Marine organisms inhabit almost around two-third of the total earth surfaces. The abundance of wide range of marine organisms makes the systematic classification of a marine organism and systematic research on marine compounds hard-hitting. Natural compounds obtained from marine organisms are used in the treatment of various diseases and disorders since ancient times. Most of the marine compounds obtained from the marine organisms are pharmacologically bioactive and they are significantly effective against various types of diseases. In the present review, the different types of seaweeds like carotenoids, polyunsaturated fatty acids, phycocolloids and sterols are discussed along with their chemical ecology. The present review will also help the researchers from various disciplines like marine and phytochemistry to understand the chemical ecology of seaweeds. This review also emphasises on the importance of various marine bioactive metabolites which are responsible for diverse pharmacological activities of different classes of seaweeds and helps in the identification lead molecules for the discovery of new drug molecule from marine sources. © 2019