The aim of this study was to determine the effect of some chemical materials on the physical and chemical properties of dental stone. Accordingly, three types of chemical materials (rosin, nigella stavia oil and sodium lauryl sulfate) were incorporated into three kinds of type III dental stone (Zeta, Elite and Dental stone) at four concentrations. The physical properties evaluated were water-powder ratio, setting time, setting expansion, compressive strength and hardness. The evaluation of chemical properties was done by the use of infrared and ultraviolet spectrophotoscopy.The results revealed that the incorporation of these chemical materials into each type of dental stone resulted in changing their evaluated physical properties; this change varies with the type, concentration of the added chemical material and type of dental stone being used. The change in the physical properties has been shown to be correlated with the changes in the chemical structure of dental stone as it became clear by comparing the ir-specra and uv-spectra of dental stone before and after the addition of the chemical materials.