equipments and reagents. Literature survey showed the use of HPLC or other chemical methods for potency estimation of Levofloxacin in pharmaceutical preparation. Yet no microbiologi- cal bioassay is available for potency determination of Levofoxacin Although HPLC is a fast method for in any pharmacopoeia. potency determination of an antibiotic it cannot determine bioactivity. However, the microbiological assay estimates both potency and bioactivity of antibiotics. Additionally. bioassay can antibiotic-resistant be used to estimate the effective dose against microbes. So. through this article we made an attempt to develop bioassay as a suitable and simple and validate a microbiological method for the quantification of Levofloxacin in pharmaceutical preparations microbiological assay mea- Compared to chemical methods, sures the true response of antibiotics on a biological system and it is used to obtain more realistie and preeise measurements of determination are potency. The bioassay methods used for potency reproducible and reliable data. the key determinants in generating Micro- which are used in quality control of the medicine biological bioassay is advantageous because the puameters that are measured with these techniques and the properties for the drug used are the same. Thus. impurities and the related substances do