Objective: The purpose of this study was to determine the force decay value of four different types of power chains used in orthodontic treatment. Materials and Methods: A sample of 20 specimens, which was divided into five piece taken from each type of the four power chains, each piece, contains six rings. The rings were placed on steel pins embedded in acrylic sheets and poured in hard stone blocks. The force of the elastomeric chains was recorded in dry state and compared to data after immersion in artificial saliva at 37 degree in bacterial incubator at time interval of 1 hour, 1 day, 1 week, 3 weeks. Results: Significant difference was found in percentage of reduction in force between the four types of the power
chains in dry field and after immersion in artificial saliva. After 3 weeks testing Morelli power chains had 41.8% reduction in force, Ultimate power chains scored 36.9% reduction in force, Dentsply power chains scored 30.8% reduction in force and Ultra- chains scored 27.2% reduction in force. Conclusion: All types of power chains showed force decay with different values after 3 weeks of testing. Choose the appropriate force value for tooth movement play important role success of orthodontic treatment.