The present study is aimed at identification of bioactive compounds and their pharmacological properties of four macroalgae (Hydropuntia edulis, Halymenia venusta, Ulva lactuca and Padina gymnospora) from the Hare Island, Tuticorin district of Tamil Nadu, India. The characterization of ethanol extracted compounds was done using GC-MS techniques. The major secondary metabolites such as alkaloids, phenol, saponins, flavonoids, steroids, terpenoids and tannins were recorded from all the algal samples. The numbers of major volatile compounds recorded in the GC-MS analysis are 32, 19, 8 and 14 in H. edulis, H. venusta, U. lactuca and P. gymnospora, respectively. All these identified compounds could be of therapeutic values for many acute and chronic diseases and disorders. These secondary metabolites belong to alkanes, aliphatic amines, aromatics, aldehydes, 1°, 2° amines and ketone groups. Many of these characterized compounds could be used for therapeutic purposes. © 2022 National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.