B Background: Elastomeric chain is one part of a fixed orthodontic appliance components used in the mechanism of tooth movement. Plaque is more easily formed around fixed orthodontic appliance components, and therefore it is necessary to control the plaque either mechanically or chemically. The usage of mouthwash (chlorhexidine gluconate and povidone iodine) as a chemical plaque control effectively inhibits Streptococcus mutans, thus prevent caries and gingivitis. lne elasticity of the elastomeric chain is presumably affected by the mouthwash usage and by the duration of stretching time, meanwhile the elasticity of elastomeric chains sold in general markets are still unexplored and not yet tested. Objective: To evaluate the effect of chlorhexidine gluconate and povidone iodine mouthwash usage and the stretching time toward the modulus elasticity of various elastomeric chains brands. Methods: EJastomeric chains (A, B and C) are divided into 4 groups (without immersion, saliva immersion, chlorhexidine gluconate immersion, povidone iodine immersion) and the duration of stretching time (24 hours, 168 hours, 336 hours, 504 hours and 672 hours). The modulus of elasticity e)ac;tomeric chains is measured by Universal Testing Machine. Three-way ANOVA and Tukey l-lSD are used to test the hypothesis. Results: The difference in the modulus of elasticity elastomeric chains (A, B and C) are affected by mouthwash usage and by the duration of stretching time. Conclusion: There are effects of mouthwash usage and the duration of stretching time toward the elastic modulus of the elastomeric chains. The elastomeric chain modulus of elasticity is lower in mouthwash immersion than in saliva immersion. Longer stretching time will increase the elastomeric chain modulus of elasticity.