The long-term durability of a photocured resin bond to groun bovine dentin with its smear layer retained was investigated. The bonding resin that was employed was composed of 5.0 wt% 2-(methacryloxy)ethyl phenyl hydrogen phosphate (phenyl-P) as a diffusion-promoting monomer, 0.5 wt% camphorquinone as a photosensitizer, and 0.5 wt% N-phenylglycine as a reducing agent in triethyleneglycol dimethacrylate. Following polymerization of the bonding resin, a composite resin was placed and photocured for 60 seconds. Prepared specimens were stored in 37 degrees C water for 1 day, 6 months, and 1 year. Measured tensile bond strengths were 6.7 MPa after 1 day of storage, 4.1 MPa after 6 months of storage, and 2.8 MPa after 1 year of storage. Examinations of the interfaces after fracture under tensile loading suggested that long-term water-immersion weakened the bonds between the photocured adhesive resin and the smear layer-retained dentin because there was insufficient diffusion of the adhesive resin through the retained smear layer.