Algae is a potential third-generation biofuel sources that can be used to produce high quality liquid fuel. The physio-chemical properties of algae depend on the species type, of which can also vary with climate, geography and environmental conditions. In this study, the pyrolysis behaviour of a brown macroalgae, Sargassum polycystum (SP), obtained along the coast of Desaru, Malaysia is characterised using a thermogravimeter. The thermal decomposition of the selected brown algae was carried out at the heating rate of 5, 10, 20 and 40 °Cmin-1. A model-fitting method, which includes the most common reaction mechanism in solid-state decomposition processes is being used to predict the kinetic parameters for Sargassum polycystum. The results showed that the Sargassum polycystum macroalgae decomposition process follows the third-order of reaction, F3 with a highest correlation value of 0.94, at 15-70 % of conversion level. The average activation energy from all heating rates is found to be 19.09 kJ/mol with a pre-exponential value of 0.537 s-1. An increase in heating rate results in the increase of activation energy and pre-exponential values.