This paper presents the experimental results of an on-going study to examine cleavage strength, particularly at the interface regions of epoxy adhesive with steel and glass reinforced epoxy (GRE) composite. The adhesion is characterised by mechanical testing of cleavage specimens. A standard specimen was modified to allow testing of hybrid joints. The effects of adhesive thickness and Various surface conditions of both adherends were examined. Among key conclusions, the study found that cleavage strength is not strongly dependent upon adhesive thickness and that polished composite gives better adhesion compared with polished steel. Test results were analysed and compared with aspects of numerical analyses. The study has also established a new methodology to test hybrid adhesive cleavage joints.