Adhesive bonding is widely accepted as one of the most efficient and practical techniques for joining fiber-reinforced polymer (FRP) adherends. Additionally, configuration of such adherends with a core material into a sandwich composite produces structural elements with superior flexural stiffness and strength. While several studies have investigated the performance of bonded joints of FRP adherends, investigations into characterization of bonded joints in sandwich composites are limited. In this paper, the results from a comprehensive experimental investigation into the fracture toughness of adhesively bonded joints, with particular emphasis on the performance of adhesive joints between sandwich beams are presented. Experimental results showed no significant dependency between the adhesive fracture toughness and the adhesive layer thickness, while the analytical and finite element results indicated that the adhesive layer properties would influence the strain energy release rate and the ratio between modes I and II in mixed-mode. (c) Koninklijke Brill NV, Leiden, 2009