The present study is focused to evaluate the effect of three different brown seaweeds on blood pressure and heart rate (HR) using spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. The seaweeds, Turbinaria ornata (T. ornata), Sargassum species (Sargassum sp.) and Padina tetrastromatica (P. tetrastromatica), were extracted in cold water and freeze-dried. Anaesthetised rats were prepared for direct blood pressure measurements with the changes in HR also being monitored. Rats were administered intravenously with the aqueous extract of the seaweeds at doses of 2.5 to 20.0 mg/kg. Concentrations of Na + , K + , Ca 2+ and Mg 2+ found in the dose of 20.0 mg/kg of the marine plant extracts were determined. Subsequently, salt solutions containing the equivalent cationic concentration found in each of the seaweed extracts were tested on Sprague-Dawley (SD) rats. All seaweeds investigated produced significant (P < 0.05) reductions in the blood pressure of both SHR and the control WKY rats. In T. ornata, significant (P < 0.05) HR reducing effect was produced. In contrast, this effect was not seen in other brown seaweeds tested. Analysis of the ionic composition present in all the extracts revealed that the salt solution with equivalent ionic content of each seaweed extract did not produce any significant decrease in blood pressure of the SD rats. In conclusion, the data obtained from the present study suggest that the aqueous extracts of T. ornata, Sargassum sp. and P. tetrastromatica may contain blood pressure lowering agents.