Anisotropic flux pinning effects due to the layered structure were inv
estigated by measuring angular dependence of magnetic hysteresis Delta
M of Y-Ba-Cu-O system at 77K as a function of the angle theta between
the field and the c-axis. The obtained results are well explained by
the anisotropic effective mass model except in the vicinity of theta =
90 degrees where the pinning character seems to change its dimension.