The fracture toughness of an epoxy-based film adhesive has been investigated using Mode I and combined Mode 1 + Mode II loadings. The opening Mode, Mode I, was realized by employing the Tapered Double Cantilever Beam (TDCB) specimen, while the mixed opening and shear modes, Mode I + Mode II, resulted from utilizing the Cracked Lap Shear (CLS) specimen. Fracture toughness was studied under conditions of constant elongation rate as well as sustained load. Furthermore, the environmental effects of both temperature (up to 70ยฐC) and water were investigated in the sustained load case. Experimental results showed that the resistance to crack growth decreased in both the uniaxial and biaxial loading cases when sustained loads were applied, compared to the case of constant elongation rate. Higher temperatures (up to 70ยฐC) in air did not cause any significant decrease in fracture toughness. However, the combination of water and temperature resulted in a significant decrease in the resistance to crack growth. Finally, mixed mode loading showed the most pronounced effect on the critical energy release rate parameter, GI,, as compared to a uniaxial, opening mode loading. The combined effect of biaxial load, temperature (up to 70ยฐC) and water resulted in a drastic decrease in fracture toughness of the studied film adhesive in comparison to uniaxial loading ambient conditions. This result is of practical importance when fracture characteristics are entered in the design considerations for an adhesively bonded structure. 998 F. FLASHNER ef al.