There are two types of method in time series analysis ; time domain method and frequency domain method. This paper is concerned with the frequency domain method which is based on the assumption that a signal can be approximated by sinusoidal waves of different frequencies. The periodogram and sample spectrum are appropriate tools for analyzing the time series. The proposed procedure has four steps which are model identification, factor analysis, calculation of periodogram and determination of major period. This four-step procedure shows good capability for cyclical factor analysis of time series.