In this paper special light diffraction phenomena and diffraction bands and rings observed when a laser beam passed through a LiKSO4 single crystal are reported. These phnomena were inverstigated in various experimental conditions. It is concluded.that the phenomena are caused by volume phase gratings with wave vectors perpendicular to c axis in LiKSO4 It is tentativly assumed that a fluctuation of the elastic strain in the direction perpendicular to c axis in LiKSO4, and therefore a related fluctuation of the dielectric tensor is produced in that direction through the photoelastic effect. As a conseqence, anisotropic volume phase gratings is formed in the crystals. No explanation is given to the appearance of secondary rings both inside and outside the main diffraction as the laser beam incident nearly normal to the c axis.