The absorption spectra of the praseodymium complex with 1-cyclopropyl-6-fluoro-1,4-dihydro-7-(4-ethyl-1-piperazinyl)-4-oxo-3-quinoline carboxylic acid hydrochloride (NNFX) has been studied by normal and derivative spectrophotometry. The complex showed maximum absorption at 350 nm at pH 6.0. The stoichiometry of the Pr-NNFX complex was calculated by the molar ratio and continuous variation methods. The ratio of Pr to NNFX was 1:3. The absorption bands of the 4f electron transitions of the praseodymium complex with NNFX are enhanced markedly, especially the wavelength at 481 nm. Using the third-derivative spectrum, the calibration graph is linear over the range 2.5 × 10^-5 - 3.5 × 10^-4 mol dm^-3 for praseodymium. The detection limits (signal-to-noise ratio of 2) is 1.4 × 10^-6 mol dm^-3. The relative standard deviation is 1.2% for 7.0 × 10^-5 mol dm^-3 of praseodymium. A method for the direct determination of praseodymium in rare earth mixtures with good accuracy and selectivity is described.