The fuel characteristics of two typical seaweeds (Enteromorpha clathrata and Sargassum natans) were studied. It was found that both the contents of volatile and ash are high, and the ash melting characteristics were different. High contents of alkali metals especially K and Na were also found in seaweed ash. The ignitions of seaweed particles were observed using a thermal microscope, which demonstrated that particle ignition proceeded in the homogeneous mode. Combustion experiments of seaweed have been conducted using a DTA-60H thermal analyzer, and the combustion processes were studied. Furthermore, the thermogravimetric mass spectrum (TG-MS) analysis was used for the gaseous products analysis during the combustion, It provided the fundamental data for the development and utilization of seaweed biomass.