Removable orthodontic appliance is one of the most popular treatments today. The ease of cleaning is an advantage of this appliance. One of the best ways to clean the tool is to use mouthwash. Some of the available mouthwashes have different composition such as fluoride, alcohol and povidone iodine which can affect the physical properties of acrylic resins that is it’s hardness. This study is a laboratory experimental. The subject of this study is 65x10x2mm Orthoplast acrylic resin that corresponding to ADA (American Dental Association) standard. The 20 acrylic resins in this study were divided into 4 groups, they are 3 types of mouthwash containing fluoride, alcohol and povidone iodine as the immersion medium and artificial saliva as the controler. The immersion done for 7 days and then the hardness is tested by using Universal Testing Machine. ANOVA analysis showed that there is no significant difference between the 4 groups. Immersion of resin acrylic for 7 days into 4 mouthwash containing fluoride, alcohol, povidone iodine and artificial saliva as controler has no influence to acrylic resin hardness.