  In this paper we report a new method for determining the thickness of the
non-edge-on disk galaxies. Our method is based on the observation comparing
with the theoretical researches of the distribution of the vertical velocity
dispersion, which is obtained from the solutions of three dimensional Poisson's
equation and the galactic dynamical equation. This method also allows us to
investigate the mass-to-light ratio of the disk. As examples, the thickness and
mass-to-light ratio of two disk galaxies, NGC 1566 and NGC 5247, which have
been extensively studied in spectroscopy, have been calculated and the results
are presented.
