Prasat Sour Prat towers (hereafter PSP) were built just in front of Royal Palace and Royal Plaza in Angkor Thom. This location is very important. However, despite the significant site locations, laterite block is used for the primary building material of PSP.
 This paper aims at a point why PSP was built with laterite blocks, and touches guess in a background in those days about a relation with a method of construction of PSP. And the features of PSP become possible to understand more by comparing with laterite structures of a Koh Ker remains group.
 The background of laterite using is important key that is understood why PSP masonry methods have some distinctive features. Especially, the processing and masonry techniques of PSP, it is possible to see the features obtained rapidly during construction.