Three cyanobacterial strains were obtained from hot springs of Northern Thailand. Morphological and physiological studies revealed that all three strains belong to genus Chroococcidiopsis. One of these strains, TS-821, was used for further studies because of its stable autotrophic growth. Its optimum temperature for growth is around 50 degrees C, and its optimum pH for growth is around 8. The strain is capable of dinitrogen fixation, and is tolerant against nitrite (5 mM), sulfite (0.6 mM) and a high concentration of carbon dioxide in the gas phase (0.4 atm). These properties indicate that the strain can be used for the conversion to organic matter of carbon dioxide produced by combustion.