Objectives: To determine the mechanical properties of Thai orthodontic elastics in comparison to imported elastics. Methods: Two different sizes groups (1/4”, 4.5 Oz and 5/16”, 4.5 Oz) of elastics from Thai brands (group-1=Thai, group-2=Thai-colored) and imported brands (group-3=Ormco, group-4=G&H) were tested for their force extension characteristic, breaking force and maximum elasticity in dry condition, and the force relaxation characteristic in wet condition. Results: At an equivalent extension, the 1/4” Thai brands and group-4 elastics generated significantly higher force (P<0.05) than group-3 elastics and the 5/16” Thai brands elastics generated significantly higher force than the imported ones. Most of the elastics did not match the force index that indicated on package when extended to 3X internal diameter, except for the 1/4” group-2 and the 5/16” group-4 elastics. The 1/4” Thai brands had significantly lower maximum elasticity than imported brands. For 5/16” elastics, group-4 had significantly higher maximum elasticity than other groups. The force relaxation pattern of all elastic brands was characterized by the significant loss of force immediately after the elastics were stretched for 15 minutes. The force continued to reduce with slower rate within 2 hours and reduced to minimal amount at the end of 24-hour period. In static test, the force reduction of the Thai elastics at 24 hours was approximately 20.0-23.0% while that of the imported elastics was 23.4-25%. In dynamic test, the force reduction of the Thai elastics at 24 hours was approximately 21.3-22.5% and the imported elastics were 24.0-26.8%. Conclusions: The mechanical properties of the Thai orthodontic elastics were comparable to those of imported brands. Thai orthodontic elastics generated greater force value and had lower force relaxation than imported orthodontic elastics. Color adding did not affect the mechanical properties of Thai orthodontic elastics.