Heparosan, the capsular polysaccharide (CPS) of some pathogenic microorganisms, play an important role in protecting bacteria from the effects of the enviromental stresses. It is almost identical to haprin and can be used as the key precursor for the preparation of bioengineered heparin and heparan sulfate. In this study, the heparosan production and growth of Escherichia coli K5 under the stresses, of osmotic, SnCl₂, organic solvents (ethanol, formamide, and hexane), and H₂O₂, were evaluated. The results indicated that the growth of E. coli K5 was not affected, while the production of heparosan was influenced under these stresses. The addition of appropriate amount of methinine, glycine, SnCl₂, and organic solvents, is helpful to heparosan production. High concentration of NaCl and H₂O₂ are unfavourable for heparosan production. Moreover, E. coli KT (with waaR gene deletion) showed the similar response to the above stress.