The interaction of lanthanide metal ions (such as Ce, Pr, Nd, Pm, Gd) with broad spectrum antibiotic Nadifloxacin has been investigated in aqueous medium at 25°C temperature and at an ionic strength of 0.2M NaClO4 by using a pH metric titration technique. The method of Calvin and Bjerrum as adopted by Irving and Rossotti has been employed to calculate the values of proton-ligand (pK) and Metal-Ligand (logK) stability constants of data obtained for Nadifloxacin complexation with rare earth metal ions. The trend in the formation constants follows the order: Pr3+ > Ce3+ > Pm3+ > Nd3+ > Gd3+