The filamentous cyanobacterium Anabaena sp. strain PCC 7120 is able to undergo cell differentiation.When facing nitrogen deficiency,5%~10% vegetative cells will develop into heterocysts for fixing nitrogen.Thus this strain is an excellent material for studying nitrogen fixation and prokaryotic cell differentiation.Isolation of high quality heterocysts is a prerequisite to study their physiological changes and regulation of related gene.However,currently available methods for isolating heterocyst are usually time-consuming,low yield and low purity,unable to fullfill the requirements of many researches.An efficient method for isolating heterocyst was developed,in which vegetative cells were effectively broken in the presence of 2 mg/mL lysozyme and 0.1% Triton X-100,allowing heterocysts to be enriched with high purity and good integrity.This method will greatly facilitate heterocyst-related studies.