Statement of Problem: Dimensional changes of denture base acrylic resins are one of the most frequent phenomena that occur during the production of the dentures in different steps of curing and different times of deflasking.Purpose: Measurement of the effect of different deflasking times on dimensional stability of acrylic resin can reduce the dimensional changes of these materials. The objective of this study was to compare these dimensional changes in different times of deflasking in two different acrylic resins (Acropars and Meliodent).Materials and Method: In this experimental study, the dimensional changes of two heat-cured poly methyl metacrylate resins (Meliodent and Acropars) were studied in different deflasking times. The initial model included one steel sheet approximately 3 mm thick, cut in the form of a dumbbell and fifty specimens of the same piece were regularly flasked and processed. Acrylic specimens, in different bench cooling times (4 hours, 12, 24, 48, 5 days) were taken out and measured in 4 areas with an accuracy of 0.01 mm using a digital caliper, subsequently, the results were studied using the One Way Anova method.Results: Dimensional changes in two types of acrylic resins (Meliodent and Acropars) showed significant differences after 5 days deflasking (P=0.000), and had the least dimensional changes. No significant differences were observed between the average dimensional changes in reference points. Keeping Meliodent acrylic resin for at least 4 hours and Acropars acrylic resin for at least 12 hours after processing can reduce dimensional changes significantly.Conclusion: Iranian specimens of Acropars acrylic resin even show smaller dimensional changes than German specimens of Meliodent acrylic resin. After 5 days, deflasking time has the least dimensional changes in both acrylic resins.Key words: Acrylic resin, Dimensional changes, Deflasking time