This research is investigating the possibility of using plaster instead of cement in some internal structural parts and non-exposed to moisture by casting (Twelve) samples dividing in four group, first group plaster of pairs concrete, second plaster of Paris with a ratio of aggregate concrete group, third normal gypsum group and finally normal gypsum with a ratio of aggregate concrete group. All of them have the same dimension (1000×150×200) mm and same reinforcement ratio. All Groups are curing in an isolated place far away of the moisture. All sample design to be the Failure as flexural failure, the process of testing divided in two ways, one for properties of material that used as explain above (Compressive Strength (f 'c) & (fcu), Splitting Tensile Strength (fct) and Flexural Strength (Modulus of Rupture) (fr)), second for samples were tested under (two-point load) for several curing period time (7, 28 and 90) days. Each period consists of three samples one from each group above. The result showed that the second group (plaster of Paris with a ratio of aggregate concrete) approximately closer or exceeded the design values. While the first group (plaster of pairs concrete) not worse when compared with the second group because of the missing aggregate.