Macroalgae were identified as third generation carbon source for bioethanol production and possess several advantages over terrestrial biomass. Hence, two common seaweeds, P. tetrastromatica and S. vulgare have been evaluated as substrates for ethanol production. They were collected from coast of the Bay of Bengal at Visakhapatnam, Andhra Pradesh, India. Samples were cleaned, dried and crushed to powder which were subjected to separate treatments with dilute sulphuric acid, sodium hydroxide and a combination of both. Based on the quantities of sugars released from these treatments, pretreatment with 1% and 2% v/v sulphuric acid for 45 min at 121˚C were chosen for P. tetrastromatica and S. vulgare respectively and the quantities of sugars released were 0.32 and 0.44 g/g. The resulting hydrolyzates were detoxified by sequential treatment with ethyl acetate and calcium oxide and were then fermented employing Saccharomyces cerevisiae strain R3DSC5 which was deposited at IMTECH, India, with accession number MTCC 12377. Ethanol yield obtained with P. tetrastromatica (0.66 g/g) during the present work is more than the highest yield (0.45 g/g) reported so far for any marine algal biomass while that obtained with S. vulgare (0.38 g/g) is on par with the highest yield (0.386 g/g) reported for other species of Sargassum. This study shows that both the seaweeds are potential sources for bioethanol production and of the two, P. tetrastromatica is better.