In vitro study was to compare retentive force between two esthetic partial denture. Acetal flexible removable partial denture and Bre-flex 2nd edition flexible removable partial denture for maxillary partially edentulous Kennedy class III modification 1 by using digital force meter.Standard experimental metal model of maxillary edentulous case (Kennedy class III with modification 1) missing right and left second premolars and first molars was fabricated to be used as master model to simulate the oral cavity. The undercuts were prepared on mesiobuccal of first premolar and distobuccal of second molar on both sides of framework, and occlusal rest seats were prepared distally on occlusal surface of first premolars and on the mesially of second molars. AKer clasp design was engaged 0.02 inch undercut for all clasps and fabricated on duplicate models, Fourteen RPD frameworks was fabricated ,divided into two equal groups.Group (A) \Seven removable partial denture fabricated from Acetal resin Group (B) Seven removable partial denture fabricated from Breflex 2nd edition.Loop was centralized in the major connector. Digital force gauge was used for both groups to measure the retention. The pulling force was gradually applied until the framework was dislodged.Results of this study showed significant difference in the retentive values between frame works with Acetal clasp and frame works with Bre-flex 2nd edition clasp were frame works With Bre-flex 2nd edition clasp showed higher retention than frame works with Acetal clasp.It was concluded that the retentive force required to remove the Acetal clasp was found lower than this required to remove Bre-flex 2nd edition clasp in Kennedy class III modification 1.