The flexural and dynamic mechanical behavior were evaluated for a new jute woven fabric/cork-reinforced polyester sandwich composite. To improve the fiber/matrix adhesion, jute fibers were treated with sodium hydroxide (NaOH) and silane prior to composite preparation. The results indicated that the flexural strength and modulus of the composites increased after the alkali and alkali + silane treatments. Similarly, dynamic mechanical parameters, such as storage and loss modulus of the sandwiches, were enhanced as a result of alkali and silane treatments due to a better fiber/matrix adhesion compared with the untreated composites. It was also shown that the damping parameter decreased after the interfacial treatments, which indicated that the energy damping efficiency decreased as the interface quality was improved.