Purpose: This study determined shear bond strength (SBS) of two composite restoratives bonded to enamel and dentin immediately (after one day) and after one month of water-storage. Methods: Eighty intact molars were sterilized with Gamma irradiation and mounted in acrylic resin bases. These were divided into two equal groups. In one group buccal enamel was ground flat while in the other buccal enamel was removed to expose flat dentin surface. Cylindrical specimens 2mm thick and 3mm diameter prepared from two composites: Filtek-Z250 (Z250) (3M/ESPE, USA) and Filtek-LS (LS) (3M/ESPE, USA) were bonded to enamel and dentin surfaces. Single Bond (3M/ESPE, USA) adhesive was used with Z250 while LS adhesive (3M/ ESPE, USA) was used with LS. Each group was subdivided into 2 subgroups. One subgroup was tested after one-day storage in distilled water at 37°C while other was tested after one-month. An Instron testing machine was used and force at failure was recorded. Mean and SDs were calculated and data statistically-analyzed using ANOVA. Results: For enamel, mean and SD for SBS in MPa measured immediately were: 18.4(1.9) and 9.4(1.3) for Z250 and LS, respectively. After one month, means and SD values were: 18.3(1.6) and 9.2(1.1) for Z250 and LS, respectively. When dentin was used, mean SBS values in MPa measured immediately were: 15.8(1.2) and 13.0(1.8) for Z250 and LS, respectively. After one month, mean and SD values were: 15.1(1.5) and 12.9(1.8) for Z250 and LS, respectively. ANOVA revealed significant difference among groups (p<.05) regarding type of composite, however, for substrate and storage time there was no significant difference in mean SBS (p>.05). Conclusions: Filtek-Z250 resulted in mean SBS values that were significantly-higher than those obtained with Filtek-LS at all test conditions. Tooth substrate type as well as storage time up to one month didn't significantly affect SBS. KEYWORDS: Composite resin, Silorane, Shear bond strength, Adhesion, Self-etching adhesive