The objective of this study was to determine the simultaneous effect of different variables on calcium hydroxide (Ca (OH) 2) nanoparticles synthesis by precipitation method, using central composite design. The used raw materials included calcium nitrate (Ca (NO3) 2.4H2O), sodium hydroxide (NaOH), and water/ethanol to dissolve the powders. In order to find optimal conditions and to achieve nanometer-sized particles, experimental design of CCD with different parameters of temperature, weight ratio of reactants, and alcohol percentage were considered at five different levels. Using experimental design of CCD and Design Expert software, a Table for 20 tests was arranged. The software was developed in order to help the user in the design and interpretation of a Multivariable Testing. In this Table, minimum and maximum of the parameters were considered as temperatures 25 and 85 ºC, weight ratio 0.5 and 1.5, and alcohol percentage 0% and 100%, respectively. Then calcium hydroxide, with the reaction of raw materials, was synthesized in an environment that contains water and alcohol. Finally, by using scanning electron microscope (SEM), X-ray diffraction, AxioVision software and Design Expert software, synthesis of nanoparticles of calcium hydroxide was approved and the influence of various parameters on the synthesis was studied.