Turbojet engines exhibit vibrations, whose amplitudes change with the life time and the operating conditions of the engine. The analysis of vibration signals in the frequency domain provides quantitative information about the dynamic behaviour of the engine and a qualitative measure of its performance. The diagnosis of engine malfunctions and the opt-imzation of maintenance costs are few examples for which the signal ana-lysis consideration becomes exceptionally important. The present paper outlines the proper applications of a vibration measuring system to a number of turbojet engines. Types of transducers, mounting location, signal conditioning and signal recording and analysis used in this deye-lopment are discussed. The paper includes a number of frequency spectra, obtained using Fast Fourier Transform (FFT) analysis for a single - shaft and a double - spool turbojet engines.