One spore-forming thermophilic bacterial strain SY-14, isolated from sewage sludge compost, showed significant capability to lyse bacterial cells. The strain was identified as Geobacillus sp. based on morphological characteristics and homology identification of 16S rDNA sequence. The optimal temperature and pH for growth were about 60 degrees C and pH 6.0-7.0 respectively. The culture supernatant of SY-14 showed lytic activity against both intact and thermal inactivated bacterial cells, and the cell lysis percentages at 6 hours were 70% and 85% respectively. The lytic activity of the culture supernatant decreased significantly after heat treatment, which inferred the lytic activity mainly derived from extracellular lytic enzymes of SY-14. The lytic activity of the culture supernatants of SY-14 increased significantly during the log phase in the batch culture process, and then decreased quickly after the maximum activity was reached. The culture supernatant of SY-14 showed lytic activity against all the five tested Gram-negative strains and some tested Gram-positive strains.