Endodontic treatment can be used to treat root canal infections.In endodontic treatment, calcium hydroxide Ca (OH)2 is com- monly used as an intracanal medicament, because of its high alkaline pH, which results in ntimicrobial properties. Nanopar- ticles are technological advancements used to improve the antimicrobial properties of Ca (OH)2.The purpose of this study is to determine the effect of particle size on the pH of Ca(OH)2 paste dissolved in various solvents, including distilled water,pro- pylene glycol,and polyethylene glycol with anL/Pratio of 0.8.A total of 24 samples of Ca(OH)2 paste were placed in a plastic tube with a height of 10 mm and a diameter of 2 mm and immersed in 10 mL distilled water in an incubator at 37o C.The pH was measured on day 1, day 7,and day 14. One-way Anova (p