Abstract: A modification was made for the potentiometric titration of the effective ingredient——levofloxacin in injections of levofloxacin hydrochloride, by addition of an appropriate amount of standard hydrochloric acid to the injection sample with its amount of substance 1.0 to 2.0 times that of the levofloxacin, and using 0.050 0 mol·L^-1 NaOH standard solution as titrant. The difference of volumes of titrants between the 3rd and 1st sudden peaks of pH in the titration curve was taken to calculate the amount of levofloxacin in the injection sample. The errors due to free HCl or free levofloxacin, which may be present in the sample, were thus eliminated. Samples of the injections taken from 4 separated batches were analyzed by this modified procedure, giving results in consistency with those found by HPLC. Values of RSDs (n=5) of the modified method were found all less than 0.30%. Test for recovery was made by standard addition method, giving values of recovery in the range of 97.6%-102%.