study was to evaluate the effects of adding chemical additives on the thermal, mechanical and chemical properties of dental plasters.This study included the evaluation of the following properties: W/P ratio, setting temperatures, setting time, setting expansion, compressive strength, surface hardness and infrared spectroscopy of the prepared samples. The results revealed that the inclusion of additives changed some of the evaluated properties, these changes correlated with the modifications seen in the Infrared spectra charts of the studied groups.It was concluded that both types of dental plasters produced setting temperatures lower than that of the dental stones (control group) and their setting temperatures were more suitable for wax pattern than that of stone but with additives the setting temperature will be increased and this belong mainly to the changes in the chemical structure of the gypsum.Also the mechanical properties of Al-Ahliyah plaster (Iraqi plaster) could be improved by the addition of some additives like rosin and gum Arabic.