In this study, the thermochemical characteristics of two types of microalgae, namely Hapalosiphon sp. and Botryococcus braunii, were investigated by use of a thermogravimetric analyzer. The low calorific value of Hapalosiphon sp. was 14.75 MJ kg(-1), which is close to that of sewage sludge or lignocellulosic biomass. However, the low calorific value of B. braunii was as high as 35.58 MJ kg(-1) due to 89% of total C and H contents in biomass. Pyrolytic results indicated that the two microalgae had similar pyrolytic temperature ranges. In addition, with increased heating rates, the pyrolytic curves of the microalgae shifted to a higher temperature. However, derivative thermogravimetric (DTG) profiles of the two microalgae are distinct, which showed that different reactions were involved in the pyrolysis process. Hapalosiphon sp. has a lower mean activation energy than B. braunii in the pyrolysis process.