The UV and vis absorption spectra of a series of substituted ethylcyanoacetate phenyl hydrazones has been studied. The band shifts with different solvents are explained in terms of solvent polarity and solute-solvent interaction. The acid-base properties of these hydrazones have been studied in order to evaluate the possibility of using them as metallochromic or chromophoric indicators. The absorption spectra are recorded in 40% ethanolic buffer solution at varying pH values. The variation in spectra with pH indicates the presence of equilibrium between the nonionized and ionized species (N-H). One or two ionization steps corresponding to the N-H and/or O-H and COOH were detected. The ionization constants were rationalized in terms of the effects of the substitutent's nature and position on the aryl group. Isomerism of these hydrazones is investigated. Potentiometrically determined ionization constants were compared with the spectrophotometrically determined values. Applications of these compounds for direct and as indicators in spectrophotometric titration with EDTA for spectrophotometric determination of lanthanides were evaluated. Beer's law was obeyed for metal ions of up to 15 ppm. Conductometric determination of lanthanides was successfully done in the working range from 150 to 1000 g.