Abstract: AIM　To investigate the photodegradation kinetic characteristics of lomefloxacin hydrochloride aqueous solution. METHODS　The HPLC method was used to determine the photodegradation kinetic parameters of lomefloxacin hydrochloride aqueous solution (10 μg.mL^-1) under various pH buffer solutions, various ionic strength of different ions and various dielectric constant conditions. RESULTS　With comparative regression analysis of linear fit，the photodegradation kinetic order of lomefloxacin hydrochloride aqueous solution was determined as n=1. The lomefloxacin hydrochloride aqueous solution is most unstable at pH 5.08-9.40 and is relatively stable at pH 2.02-5.08 and 9.40-11.10. The higher the ionic strength in lomefloxacin hydrochloride aqueous solution, the higher the photodegradation kinetic rate constant is. The chloride ion has important effect on photodegradation in aqueous solution of lomefloxacin and results in producing chlorine derivative as the highest photodegradation product. As the dielectric constant of solution increased, the photodegradation kinetic rate constant was also increased. CONCLUSION　It was found that the photodegradation of lomefloxacin followed apparent first-order kinetics. The photodegradation kinetic rate was affected by pH remarkably and showed positive correlation with ionic strength and dielectric constant.