Abstract: Spectral analysis of acoustic emissions (A. E. singals which occured in marble and galbbro specimens during uniaxial compression has been performed, frequency window analysed in present study ranging from 25 kHz to 387 kHz. In experiments we record the waveform of A. E. signals by using of a high speed data aquisition system, and analyse the amplitude spectrum of 32 A. E. events in virtue of FFT routine.
Very little is known about the frequency contents of A. E. signals in spectrum of A. E. and studying of the stress dependence of those spectrum will take us one step close to the actual mechanism of acoustical emission events in rocks. In present paper, three parameters （dominant frequency fAmaX, number of peak in spectrum n and energy of an individual A. E. signal IE） are using to characterize the A. E. signals statistically. The results as follows:
（1） A. E. signals detected on the surface of the rock specimen contain various frequency components. Their spectrum exhibit harmonic characteristics. For the marble and gab-bro specimens with the dimension of 2.5-5 cm in diameter and of 5-10 cm in length, the main energy distribute in the frequency range of 40-110 kHz.
（2） There is no obvious deference in frequency contents between marble and gabbro, but it seems to exist somewhat size dependence of spectrum.
（3） Spectrum of A. E. signals in rock varies randomly with the increase of stress, in other words, no remarkable stress dependence of spectrum was detected.