Optical rotatory dispersion of LiKSO4 crystal was pleasured at room temperature. The "crystal" nsodel of optical rotation fits well to the experimental results. In the temperature range from -180℃ to 680℃, four phase transitions were observed by means of optical rotation measurement: Phase F3 Phase F2 Phase F1 Phase X670℃→Phase α. The two transitions at low temperatures show obvious temperature hysteresis. All the transition temperatures are different from sample to sample. The relation between the transition sequence shown above and the data reported in literatures is discussed.