The marine macroalgae green tides occurring frequently produced a great quantity of macroalgal wastes from 2007 to 2011 in China. The pyrolytic characteristics and kinetics of one kind of marine green tide macroalgae, Enteromorpha prolifera, was investigated by the thermogravimetric analysis method at heating rates of 10, 20, 30, 40, 50°C/min. The corresponding activation energy E and the pre-exponential factor A were calculated and the mechanism functions were determined by double extrapolation and Flynn-Wall-Ozawa methods based on the thermogravimetric data. The results show that the optimum mechanism can be described by the Zhuralev, Lesokin, and Tempelmen equation (G(α) = {[1/(1 − α]1/3 − 1}2) for E. prolifera in pyrolysis temperatures that range from 240 to 290°C, and the thermolysis mechanism is a three-dimensional diffusion process in the main pyrolysis process. It indicates that E. prolifera has low thermal stability for pyrolysis and is a potential biomass energy resource.