Among the geomagnetic secular variations of several decades, the variation with a period of about 60 years, is considered to be one of the most predominant features. Spherical harmonic analyses were made of the annual mean values of the three components at 21 magnetic observatories, and the annual sets of the Gauss coefficients were obtained during the interval from 1910 to 1983. Then the time series of the Gauss coefficients were analyzed by the Sompi spectral method. It turned out that 1) The amplitudes of the Gauss coefficients vary with periods of approximately 60 years. 2) The “sixty year variation” is of internal origin. 3) The variation occurs on a global scale. 4) The variation is commonly observed in almost all the Gauss coefficients of spherical harmonic degree up to 4.5) The variation observed in each mode varies roughly in phase (or antiphase) except a few modes.