Adhesives used in aircrafts degrade because of moisture. To understand the fractures at the adhesive interface, moisture diffusion coefficients must be estimated, which is challenging and has not yet been reported. In this study, we prepared double cantilever beam specimens using an aluminum adherend and epoxy adhesives, immersed them in a hot bath, and observed the resultant fracture surfaces. The distance of moisture penetration at the interface was estimated from the fracture morphology, and the diffusion coefficient for moisture penetration into the adhesive was measured using a bulk immersion test. Both these values were used to determine the moisture diffusion coefficient at the adhesive interface, which was ∼3 times higher than that of the bulk. The relationship between immersion temperature and moisture diffusion coefficient of the adhesive interface adhered to the Arrhenius equation, as same as that of bulk. •Fracture surfaces of immersed DCB shows interfacial fracture at the edge owing to moisture intrusion.•The moisture diffusion coefficient on the adhesive interface was calculated from the observation of the fracture surface.•The moisture diffusion coefficient at the adhesive interface, which was ∼3 times higher than that of the bulk.•The activation energy for moisture diffusion in the adhesive interface and the bulk was the same.•The effect of surface treatment on the water diffusion coefficient of the adhesive interface in the adherend was unclear.