This paper presents a case study of foundation of an inclined independent masonry tower in Angkor. One of the Prasat Sour Prat towers had been dismantled before reconstruction for conservation. The foundation was inclined as the same as the upper structure of the tower and spreading outwards. The inclination was considered caused by foundation failure with some differential settlements of the ground. During dismantling, the soil layers exposed on the trenched section were found rather horizontal than the inclined state that had been expected. Laterite blocks of step slope stones was found to have slid down along the soil mound of the foundation. The mechanism might have been caused by weakening of soil strength by wetting ground. Without dismantling, the real mechanism of the inclination was never known as well as the corresponding counter measures.